Electromagnetic noise suppressor, article with electromagnetic noise suppressing function, and their manufacturing methods

ABSTRACT

An electromagnetic noise suppressor of the present invention includes a base material  2  containing a binding agent and a composite layer  3  formed by integrating the binding agent that is a part of the base material  2  and the magnetic material. This electromagnetic noise suppressor has high electromagnetic noise suppressing effect in the sub-microwave band, and enables it to reduce the space requirement and weight. The electromagnetic noise suppressor can be manufactured by forming the composite layer  3  on the surface of the base material  2  by physical vapor deposition of the magnetic material onto the surface of the base material  2.  The article with an electromagnetic noise suppressing function of the present invention is an electronic component, a printed wiring board, a semiconductor integrated circuit or other article of which at least a part of the surface is covered by the electromagnetic noise suppressor of the present invention.

TECHNICAL FIELD

The present invention relates to an electromagnetic noise suppressorthat suppresses electromagnetic noise, an article with anelectromagnetic noise suppressing function, and a method ofmanufacturing the same.

BACKGROUND ART

In recent years, as the use of the Internet increases, electoronicapparatuses that use CPUs running at high clock frequencies in thesub-microwave band (0.3 to 10 GHz), electronic apparatuses that use highfrequency bus, and telecommunication apparatuses that utilize radiowaves have been increasing, such as personal computers, home applianceshaving information processing functions, wireless LAN,bluetooth-equipped apparatuses, optical module, mobile telephones,mobile information terminals and intelligent road traffic informationsystem. This trend leads to a society of ubiquitous computing thatrequires devices of higher performance with high-speed digitalinformation processing function and low-voltage driving. However, assuch apparatuses become popular, concerns have been increasing on theproblems related to the electromagnetic interference such asmalfunctions of the apparatus that emit electromagnetic radiation orother apparatuses and health threats to the human body. For this reason,such an apparatus is required to minimize the emission of unnecessaryelectromagnetic radiation so as not to affect its own operation and thatof other apparatuses and not to cause adverse effect on the human body,and to operate without malfunction when subjected to electromagneticradiation emitted by other apparatuses. Measures to prevent suchelectromagnetic interference include the use of an electromagneticradiation shielding material that reflects electromagnetic radiation andthe use of an electromagnetic absorbing material.

As the means for preventing electromagnetic interference betweenelectronic apparatuses, electromagnetic radiation shielding material isprovided on the surface of the housing of the electronic apparatus orbetween electronic apparatuses so as to block electromagnetic radiation(inter-system EMC). As a means for preventing electromagneticinterference within an electronic apparatus, electronic components andcircuits are covered with electromagnetic radiation shielding materialso as to prevent the electronic components and circuits from interferingwith each other and resulting in malfunction, and suppressing theprocessing speed from decreasing and signal waveform from beingdistorted (intra-system EMC).

It has also been proposed to suppress the generation of electromagneticnoise by providing electromagnetic noise suppressing measures toelectronic components that are the sources of the electromagnetic noiseor to suppress the interference between signals thereby to improve thetransmission characteristic in near-field environments such as within anelectronic apparatus (micro EMC).

Electronic apparatuses and electronic components are recently requiredto have higher performance and be smaller and lighter in weight, and theelectromagnetic noise suppressor used in these apparatuses or componentsis also required to have high electromagnetic noise suppressing effectsin a high-frequency band such as sub-microwave band, become smaller andlighter in weight, and be easy to carry out by the work which takesmeasures with electromagnetic noise suppressing measures.

Conventional electrically conductive shield strengthens electromagneticcoupling due to the reflection from unnecessary radiation source.Therefore, it is said to be effective to suppress the unnecessaryradiation source by making use of magnetic loss of magnetic material,namely the imaginary part of complex permeability μ″. Japanese PatentApplication, First Publication No. Hei 9-93034 discloses anelectromagnetic radiation absorbing material made by adding about 95% byweight of such a magnetic powder to an organic binding agent asthickness of flaked powder of soft magnetic material is smaller than theskin depth, having sufficiently high aspect ratio with the magneticmaterial turned to be non-conductive. The electromagnetic radiationabsorbing material is said to have high electromagnetic radiationabsorbing property and flexibility. In this example, an electromagneticradiation absorbing material provided with a backing made of a copperplate is used for evaluation, and thickness of the electromagneticradiation absorbing material and the copper plate used for measurementcombined is 2 mm.

However, thickness of the electromagnetic radiation absorbing materialand the copper plate combined is 2 mm and sheet thickness of theelectromagnetic radiation absorbing material excluding the copper plateis as thick as 1 mm or more, and is heavy because 95% by weight of theelectromagnetic radiation absorbing material consists of ferromagneticmaterial such as iron. Therefore, it cannot be said that weightreduction has been achieved. It is also not sufficiently robust andflexible since its content of organic binding agent is small. Moreover,the flaked powder of soft magnetic material is expensive because itrequires tedious processes to form the soft magnetic material in flakesand making the surface not electrically conductive. The electromagneticradiation absorbing material that uses the flaked powder of softmagnetic material in a large amounts also is expensive and cannotsatisfy the needs of industry.

Japanese Patent Application, First Publication No. Hei 9-181476discloses an electromagnetic radiation absorbing material made byforming a layer of a ferromagnetic element and ceramic element bymagnetron sputtering on a substrate, and annealing at a low temperatureso as that ultra-fine crystal of ferromagnetic material precipitates inthe ceramic phase of high resistivity thereby achieving isolation. It isclaimed that the electromagnetic radiation absorbing material has highelectrical resistance in a high-frequency band from 100 MHz to 10 GHz,capability to suppress the reflection of electromagnetic radiation dueto eddy current and a large value of imaginary part of complexpermeability μ″, thus resulting in high electromagnetic radiationabsorbing property.

It is said that the electromagnetic radiation absorbing materialrequires heat treatment at a high temperature in order to form theultra-fine crystal of ferromagnetic material in the ceramic phase. Inthis example, a film is formed from ceramic and ferromagnetic elementson a glass slide by a RF magnetron sputtering method, and heat treatmentis applied at a temperature from 200 to 350° C., thereby forming theultra-fine crystal of ferromagnetic material. It cannot be avoided touse an organic film that has high heat resistance as the organic film ofthis electromagnetic radiation absorbing material, although the ceramicphase and ultra-fine crystal of ferromagnetic material phase are formedon the organic film. Since the organic film which has high heatresistance is expensive, the electromagnetic radiation absorbingmaterial that uses it is also expensive. Moreover, even when theultra-fine crystal of ferromagnetic material is formed on the organicfilm having high heat resistance, there is a significant difference inthe thermal expansion coefficient between the organic film and theceramic phase that causes cracks, resulting in a material far from beingflexible or tough.

As for the electromagnetic noise suppressor, it has been proposed tomake a thin electromagnetic noise suppressor that has electromagneticnoise suppressing effect in the sub-microwave band by ferrite platingtechnology (Masaki ABE et al., Proceedings of the 131^(st) Conference,pp 25-31, Jul. 4, 2003; The Magnetics Society of Japan).

The electromagnetic noise suppressor based on the ferrite platingtechnology is made by applying a reaction solution of chlorides of iron,nickel and zinc and an oxidation liquid comprising sodium nitrate andammonia acetate on a polyimide sheet placed on a rotary substrate, so asto form a ferrite compound film having a thickness of 3 μm by plating bya spin spray process. This electromagnetic noise suppressor has, despitesmaller thickness, electromagnetic noise suppressing effect similar tothat of the conventional electromagnetic noise suppressor made in asheet 50 μm thick by dispersing the fine particles of flake-shaped metalin the organic binding agent, and is said to be advantageously appliedto small electoronic apparatuses.

However, thickness of the ferromagnetic layer of this electromagneticnoise suppressor is from 3 to 11 μm and power loss of theelectromagnetic noise suppressor at 1 GHz is about 0.2 even when formedwith a large thickness, resulting in insufficient electromagnetic noisesuppressing effect in low frequency portion of the sub-microwave band.When the thickness of the ferromagnetic material increases, sufficientrobustness and flexibility cannot be achieved since the ferrite layerformed on the polyimide is hard and does not contain organic bindingagent. Moreover, since it is made in a wet process, it requires tediousprocesses such as removal of impurities and drying, and does not satisfythe needs of industry.

It has also been proposed to make an electromagnetic noise suppressorcomprising a ultra-fine crystal of a ferromagnetic material filmcontaining alumina ceramics phase and ultra-fine crystal phase offerromagnetic material of iron or cobalt (Shigehiro OHNUMA et al.,Proceedings of the 131^(st) Conference, pp 17-24, Jul. 4, 2003; TheMagnetics Society of Japan). This proposal relates to an electromagneticnoise suppressor having a thickness of 1 μm made by forming layer offerromagnetic element and ceramic element by high-frequency magnetronsputtering on a substrate, annealing at a low temperature so thatultra-fine crystals of ferromagnetic material precipitate in the ceramicphase of high resistivity and dividing by forming a slit so as toincrease resistivity of the film further, which is claimed to have highnoise suppressing effect.

However, this electromagnetic noise suppressor has electromagneticradiation absorbing property similar to that of the conventionalelectromagnetic noise suppressor made in a sheet 50 μm thick bydispersing the fine particles of flake-shaped metal in the organicbinding agent and power loss of about 0.2 at 1 GHz, resulting ininsufficient electromagnetic noise suppressing effect in the effectivefrequency band. Also, it is necessary to apply heat treatment in orderto form the ultra-fine crystals of ferromagnetic material in the ceramicphase and a micro slit must be formed by photolithography or by means ofa dicing saw in order to increase the resistivity of the thin magneticfilm, making the process tedious. Also because it is a thin ceramicfilm, it is prone to cracks, resulting in a material which is far frombeing flexible or robust.

Electrical and electoronic apparatuses are required to have flameretarding property (in accordance with UL94 V-0, V-1 or VTM-0, VTM-1) toensure safety, and the electromagnetic noise suppressor used in such anapparatus is also required to have flame retarding property (inaccordance with UL94 V-0, V-1 or VTM-0, VTM-1). The UL refers tostandards specified by Underwriters Laboratory Inc. of the United Statesfor the safety of electrical apparatuses, and UL94 is a standardrelating to flame retarding property. Flame retarding property specifiedin UL94 V-0, V-1 or VTM-0, VTM-1 will hereinafter be referred to simplyas flame retarding property.

Japanese Patent Application, First Publication No. 2000-196281 disclosesan electromagnetic radiation absorbing material that has flame retardingproperty made by applying a coating material containing a high-polymerbinding agent, a soft magnetic material powder and a phosphorus-basedflame retarding agent on a supporting body thereby forming anelectromagnetic radiation absorbing layer.

However, in the case in which the soft magnetic material powder is usedas the electromagnetic radiation absorbing material, a large quantity ofthe soft magnetic material powder must be used in order to achievesufficient effect of absorbing electromagnetic radiation, the amountbeing 100 parts by weight for 5 to 12 parts by weight of thehigh-polymer binding agent. Also, in the case in which the soft magneticmaterial powder is used as the electromagnetic radiation absorbingmaterial, the electromagnetic radiation absorbing layer must be madethick in order to achieve sufficient effect of absorbing electromagneticradiation. As a result, the electromagnetic radiation absorbing materialbecomes heavy because the electromagnetic radiation absorbing layer hasa high specific gravity and is thick. Also there has been a problem inthat it is difficult to reduce the space requirement because theelectromagnetic radiation absorbing layer is provided on the supportmaterial and is thick. Moreover, since the soft magnetic material powderis a metal powder, it can easily generate heat and ignite. Therefore, alarge amount of the flame retarding agent must be added in order for theelectromagnetic radiation absorbing material to exhibit sufficient flameretarding property. Also, because the electromagnetic radiationabsorbing material consists mostly of soft magnetic material powder witha small proportion occupied by the polymer binding agent, it is lessflexible and is brittle.

Japanese Patent Application, First Publication No. 2002-84091 proposesan electromagnetic radiation absorbing sheet formed by stacking anelectromagnetic radiation absorbing material consisting of ferritepowder or soft magnetic material powder mixed in a resin as anelectromagnetic radiation absorbing material that has flame retardingproperty and a flame retarding material.

However, in the case of a ferrite powder or the soft magnetic materialpowder is used as the electromagnetic radiation absorbing material, alarge amount of the material must be used in order to achieve sufficienteffect of absorbing electromagnetic radiation, the amount being about90% by weight of the electromagnetic radiation absorbing material. Also,when ferrite powder or the soft magnetic material powder is used as theelectromagnetic radiation absorbing material, the electromagneticradiation absorbing layer must be made thick in order to achievesufficient effect of absorbing electromagnetic radiation. As a result,the electromagnetic radiation absorbing material is heavy because theelectromagnetic radiation absorbing layer has a high specific gravityand is thick. Also, there has been a problem in that it is difficult toreduce the space requirement because the electromagnetic radiationabsorbing material has a large thickness. Moreover, since ferrite powderand soft magnetic material powder can easily generate heat and ignite,it may be difficult to prevent it from burning simply by laminating aflame retarding material. Also, because the electromagnetic radiationabsorbing material consists mostly of ferrite powder and soft magneticmaterial powder with a small proportion occupied by a resin, it is lessflexible and is brittle.

Japanese Patent Application, First Publication No. Hei 7-212079discloses an electromagnetic interference suppressor that comprises anelectrically conductive support member and an insulating soft magneticmaterial layer provided on at least one surface of the electricallyconductive support member, where the insulating soft magnetic materiallayer contains soft magnetic material powder and an organic bindingagent.

This electromagnetic interference suppressor has a large thickness andcontains much magnetic material in the entire region of the insulatingsoft magnetic material layer, and is therefore heavy. It is also notsufficiently tough and flexible, and does not meet the requirements forhigh-density packaging.

With the background described above, an object of the present inventionis to provide an electromagnetic noise suppressor that has highelectromagnetic noise suppressing effect in the sub-microwave band,requires small installation space and is light in weight, articles suchas electronic components and printed wiring board that are provided withelectromagnetic noise suppressing means and a manufacture method thatthese can be manufactured easily.

Another object of the present invention is to provide an electromagneticnoise suppressor that is flexible and has high strength.

Still another object of the present invention is to provide anelectromagnetic noise suppressor that has a sufficient flame retardingproperty.

A further object of the present invention is to provide anelectromagnetic noise suppressor that also has an electromagneticradiation shielding property.

DISCLOSURE OF INVENTION

The electromagnetic noise suppressor of the present invention includes abase material containing a binding agent and a composite layer formed byintegrating the binding agent that is a part of the base material and amagnetic material. This electromagnetic noise suppressor has highelectromagnetic noise suppressing effect in the sub-microwave band andenables it to reduce the space requirement and weight.

The composite layer is desirably a layer formed by physical vapordeposition of a magnetic material on the base material surface. In sucha composite layer, the magnetic material is dispersed in the bindingagent so that the magnetic material and the binding agent are integratedto provide high electromagnetic noise suppressing effect. The compositelayer does not contain impurity ions so that there is no possibility ofdamage to the electronic circuit by the impurity ions.

The electromagnetic noise suppressor of the present invention hasmaximum transmission attenuation of electromagnetic radiation per unitthickness of the composite layer preferably in a range from −0.5 to −500dB/μm. In such a composite layer, the magnetic material is dispersed inthe binding agent so that the magnetic material and the binding agentare integrated to provide high electromagnetic noise suppressing effect.

The electromagnetic noise suppressor of the present invention hasmaximum transmission attenuation of electromagnetic radiation,preferably in a range from −10 to −50 dB. Such an electromagnetic noisesuppressor has even higher electromagnetic noise suppressing effect.

The electromagnetic noise suppressor of the present invention hasmaximum reflective attenuation at the frequency where it exhibitsmaximum transmission attenuation of electromagnetic radiation,preferably in a range from −6 to −50 dB. Such an electromagnetic noisesuppressor has even higher electromagnetic noise suppressing effect.

The electromagnetic noise suppressor of the present invention has powerloss at 1 GHz preferably in a range from −0.3 to −0.65 dB. Such anelectromagnetic noise suppressor has even higher electromagnetic noisesuppressing effect.

The thickness of the composite layer is preferably in a range from 0.005to 20 μm, more preferably from 0.005 to 3 μm, even more preferably from0.005 to 1 μm, and most preferably in a range from 0.005 to 0.3 μm. Suchan electromagnetic noise suppressor has further higher electromagneticnoise suppressing effect and enables it to reduce the space requirementand weight.

The electromagnetic noise suppressor of the present invention hasspecific gravity desirably in a range from 0.9 to 1.5. Such anelectromagnetic noise suppressor has a composite layer thin enough. Insuch a composite layer, the magnetic material is dispersed in thebinding agent so that the magnetic material and the binding agent areintegrated to provide high electromagnetic noise suppressing effect.

The electromagnetic noise suppressor of the present invention may alsobe constituted from a plurality of electromagnetic noise suppressorsstacked one on another. Such an electromagnetic noise suppressor haseven higher electromagnetic noise suppressing effect due to larger totalamount of the magnetic material.

The binding agent is preferably a resin or a rubber. When a resin or arubber is used for the binding agent, an electromagnetic noisesuppressor that is flexible and has high strength can be made.

Alternatively, the binding agent is preferably a hardening resin. Thebinding agent, when the binding agent comprises a hardening resin, themagnetic material can be dispersed in the binding agent that has not yetcured more uniformly. After the binding agent has cured, the magneticmaterial does not crystallize into fine particles, and such a compositelayer can be obtained where the binding agent and the magnetic materialare integrated at the atomic level.

The elastic modulus in shear of the binding agent is preferably in arange from 1×10⁴ to 1×10¹⁰ Pa, and more preferably in a range from 1×10⁴to 5×10⁷ Pa. When the elastic modulus in shear of the binding agent isset in this range, the magnetic material is dispersed in the bindingagent so that the binding agent and the magnetic material areintegrated, thereby forming a composite layer having highelectromagnetic noise suppressing effect.

It is preferable that the electromagnetic noise suppressor of thepresent invention further has a thermally conductive layer containing athermally conductive filling agent. Such an electromagnetic noisesuppressor has a high heat dissipating property.

It is preferable that the electromagnetic noise suppressor of thepresent invention further has a support layer. Such an electromagneticnoise suppressor has high flexibility and high strength, and is easierto handle, even when the base material that constitutes the compositelayer is made thinner.

The base material preferably contains a flame-retarding agent ofnon-halogen and non-antimony material (hereinafter referred to asnon-halogen, non-antimony flame retarding agent). The electromagneticnoise suppressor containing such a base material has sufficient flameretarding performance.

Alternatively, it is preferable that the electromagnetic noisesuppressor of the present invention further have a flame retarding resinlayer. Such an electromagnetic noise suppressor has sufficient flameretarding performance.

The base material preferably contains an electrically conductive filler.The electromagnetic noise suppressor having such a base material haselectromagnetic radiation shielding property as well, and does notaggravate electromagnetic coupling due to the reflection ofelectromagnetic radiation.

The electrically conductive filler is preferably an electricallyconductive fine powder of at least one kind selected from a groupconsisting of metal powder, metal fiber, metal-coated fine particles,fine carbon particles and carbon nano-tubes. The base materialcontaining such an electrically conductive fine powder has higherelectromagnetic radiation shielding property.

Alternatively, it is preferable that the electromagnetic noisesuppressor of the present invention further have an electricallyconductive layer. Such an electromagnetic noise suppressor haselectromagnetic radiation shielding property as well, and does notaggravate electromagnetic coupling due to the reflection ofelectromagnetic radiation.

The electrically conductive layer is preferably at least one kindselected from the group consisting of metal foil, fabric of metalfibers, fabric of electrically conductive fibers, interlaced metalwires, interlaced electrically conductive fibers, organic polymer layercontaining an electrically conductive filling agent dispersed thereinand electrically conductive film. The electromagnetic noise suppressorhaving such an electrically conductive layer has further higherelectromagnetic radiation shielding property.

The electrically conductive film preferably includes a support film anda metal layer having a thickness in a range from 5 to 500 nm formed onthe support film by physical vapor deposition. The electromagnetic noisesuppressor having such an electrically conductive film has highflexibility and enables it to reduce the space requirement and weight.

The metal layer is preferably formed by an opposing target typemagnetron sputtering process. The opposing target type magnetronsputtering process is highly evaluated in terms of environmentconservation and productivity.

The base material preferably contains a dielectric powder. Theelectromagnetic noise suppressor having such a base material achievesimpedance matching with the space and makes the undesirable reflectionof electromagnetic radiation less likely to occur.

The dielectric material powder is preferably at least one kind selectedfrom a group consisting of barium titanate-based ceramic, zirconiumtitanate-based ceramic and lead perovskite-based ceramic. The basematerial containing such a dielectric material powder has higher effectof suppressing the undesirable reflection of electromagnetic radiation.

The method of manufacturing the electromagnetic noise suppressor of thepresent invention includes a vapor deposition process of physicallyvapor-depositing a magnetic material onto the surface of a base materialcontaining a binding agent to form a composite layer on the surface ofthe base material. Such a manufacturing method makes it easily tomanufacture the electromagnetic noise suppressor of the presentinvention that has the composite layer constituted from the bindingagent and the magnetic material integrated together.

In the method of manufacturing the electromagnetic noise suppressor ofthe present invention, it is desirable that the magnetic material beapplied by physical vapor deposition on the surface of the base materialcontaining the binding agent by means of opposing target type magnetronsputtering process. Such a manufacturing method causes the magneticmaterial to be dispersed in the binding agent so that the magneticmaterial and the binding agent are integrated, thereby making itpossible to easily manufacture the electromagnetic noise suppressorhaving further higher electromagnetic noise suppressing effect.

In the method of manufacturing the electromagnetic noise suppressor ofthe present invention, it is desirable that the magnetic material beapplied to the surface of the base material containing the binding agentby physical vapor deposition with particle energy in a range from 5 to1000 eV. Such a manufacturing method causes the magnetic material to bedispersed in the binding agent so that the magnetic material and thebinding agent are integrated, thereby making it possible to easilymanufacture the electromagnetic noise suppressor having further higherelectromagnetic noise suppressing effect.

In the method of manufacturing the electromagnetic noise suppressor ofthe present invention, it is desirable that the amount of the magneticmaterial deposited is in a range from 0.5 to 200 nm in terms ofthickness of the magnetic material film. Such a manufacturing methodcauses the magnetic material to be dispersed in the binding agent sothat the magnetic material and the binding agent are integrated, therebymaking it possible to easily manufacture the electromagnetic noisesuppressor having further higher electromagnetic noise suppressingeffect.

Another method of manufacturing the electromagnetic noise suppressor ofthe present invention includes a stack fabricating process offabricating a stack by stacking other layers on a base materialcontaining a binding agent, and a vapor deposition process of physicallyvapor-depositing a magnetic material onto the surface of the basematerial containing a binding agent to form a composite layer on thesurface of the base material. Such a manufacturing method makes it easyto manufacture the electromagnetic noise suppressor of the presentinvention that has the composite layer constituted from the bindingagent and the magnetic material integrated together and another layer.

An article with an electromagnetic noise suppressing function of thepresent invention is an article with at least a part of the surfacethereof covered by the electromagnetic noise suppressor of the presentinvention. The article with an electromagnetic noise suppressingfunction enables it to dispose the electromagnetic noise suppressor in asmall space near a noise source and efficiently suppress electromagneticnoise in a sub-microwave band.

A method of manufacturing the article with an electromagnetic noisesuppressing function of the present invention includes a coating processof coating at least a part of the surface of the article with a bindingagent and a vapor deposition process of physically vapor-depositing amagnetic material onto the surface of a base material to form acomposite layer on the surface of the base material. Such amanufacturing method makes it easy to manufacture the article with anelectromagnetic noise suppressing function that can efficiently suppresselectromagnetic noise in a sub-microwave band.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an image of a composite layer of an electromagnetic noisesuppressor of the present invention observed with a high-resolutiontransmission electron microscope.

FIG. 2 is a schematic diagram showing the vicinity of the compositelayer in an example.

FIG. 3 is a SEM image of a base material coated with magnetic materialby physical vapor deposition in a sectional view.

FIG. 4 is a laser microscope image of the surface of the base materialcoated with magnetic material by physical vapor deposition (73.5 μmalong one side, in perspective view).

FIG. 5 is a laser microscope image of measuring the section of the basematerial coated with magnetic material by physical vapor deposition.

FIG. 6 is a laser microscope image of the surface of the base materialbefore being coated with magnetic material by physical vapor deposition(73.5 μm along one side, in perspective view).

FIG. 7 is a laser microscope image of measuring the section of the basematerial before being coated with magnetic material by physical vapordeposition.

FIG. 8 is a schematic sectional view showing an example ofelectromagnetic noise suppressor of the present invention.

FIG. 9 is a schematic sectional view showing another example of theelectromagnetic noise suppressor of the present invention.

FIG. 10 is a schematic sectional view showing another example of theelectromagnetic noise suppressor of the present invention.

FIG. 11 is a schematic sectional view showing another example of theelectromagnetic noise suppressor of the present invention.

FIG. 12 is a schematic sectional view showing another example of theelectromagnetic noise suppressor of the present invention.

FIG. 13 is a schematic sectional view showing another example of theelectromagnetic noise suppressor of the present invention.

FIG. 14 is a schematic sectional view showing another example of theelectromagnetic noise suppressor of the present invention.

FIG. 15 is a schematic sectional view showing another example of theelectromagnetic noise suppressor of the present invention.

FIG. 16 is a schematic sectional view showing another example of theelectromagnetic noise suppressor of the present invention.

FIG. 17 is a perspective view of a camera module that is an example ofan article with an electromagnetic noise suppressing function of thepresent invention.

FIG. 18 is a sectional view of a camera module that is an example of anarticle with an electromagnetic noise suppressing function of thepresent invention.

FIG. 19 is a sectional view of a printed wiring board with electroniccomponents mounted thereon as an example of an article with anelectromagnetic noise suppressing function of the present invention.

FIG. 20 is a schematic diagram of a setup for measuring theelectromagnetic noise suppressing characteristic.

FIG. 21 is a graph showing transmission attenuation and reflectionattenuation of the electromagnetic noise suppressor in a frequency rangefrom 0.05 to 3 GHz of example 5, with intensity of incomingelectromagnetic radiation being set to reference (0).

FIG. 22 is a graph showing transmission attenuation and reflectionattenuation of the electromagnetic noise suppressor in a frequency rangefrom 0.05 to 18 GHz of Example 6, with intensity of incomingelectromagnetic radiation being set to reference (0).

FIG. 23 is a graph showing transmission attenuation and reflectionattenuation of the electromagnetic noise suppressor in a frequency rangefrom 0.05 to 18 GHz of Example 7, with intensity of incomingelectromagnetic radiation being set to reference (0).

FIG. 24 is a graph showing transmission attenuation and reflectionattenuation of the electromagnetic noise suppressor in a frequency rangefrom 0.05 to 3 GHz of Comparative Example 2, with intensity of incomingelectromagnetic radiation being set to reference (0).

FIG. 25 is a graph showing transmission attenuation and reflectionattenuation of the electromagnetic noise suppressor in a frequency rangefrom 0.05 to 18 GHz of Comparative Example 3, with intensity of incomingelectromagnetic radiation being set to reference (0).

FIG. 26 is a graph showing transmission attenuation and reflectionattenuation of the electromagnetic noise suppressor in a frequency rangefrom 0.05 to 3 GHz of Comparative Example 4, with intensity of incomingelectromagnetic radiation being set to reference (0).

FIG. 27 is a graph showing power loss characteristic of theelectromagnetic noise suppressor in a frequency range from 0.05 to 3 GHzof Example 8.

FIG. 28 is a graph showing power loss characteristic of theelectromagnetic noise suppressor in a frequency range from 0.05 to 3 GHzof Example 9.

FIG. 29 is a graph showing power loss characteristic of theelectromagnetic noise suppressor in a frequency range from 0.05 to 3 GHzof Example 10.

FIG. 30 is a graph showing power loss characteristic of theelectromagnetic noise suppressor in a frequency range from 0.05 to 3 GHzof Comparative Example 5.

FIG. 31 is a graph showing power loss characteristic of theelectromagnetic noise suppressor in a frequency range from 0.05 to 3 GHzof Comparative Example 6.

FIG. 32 is a graph showing power loss characteristic of theelectromagnetic noise suppressor in a frequency range from 0.05 to 3 GHzof Comparative Example 7.

FIG. 33 is a graph showing the frequency characteristic of reflectingattenuation of transmitted noise in the electromagnetic noise suppressorof Example 17.

FIG. 34 is a graph showing the frequency characteristic of power loss oftransmitted noise in the electromagnetic noise suppressor of Example 17.

FIG. 35 is a graph showing the frequency characteristic of reflectingattenuation of transmitted noise in the electromagnetic noise suppressorof Example 18.

FIG. 36 is a graph showing the frequency characteristic of power loss oftransmitted noise in the electromagnetic noise suppressor of Example 18.

FIG. 37 is a graph showing the frequency characteristic of reflectingattenuation of transmitted noise in the electromagnetic noise suppressorof Example 19.

FIG. 38 is a graph showing the frequency characteristic of power loss oftransmitted noise in the electromagnetic noise suppressor of Example 19.

FIG. 39 is a graph showing the frequency characteristic of reflectingattenuation of transmitted noise in the electromagnetic noise suppressorof Example 20.

FIG. 40 is a graph showing the frequency characteristic of power loss oftransmitted noise in the electromagnetic noise suppressor of Example 20.

FIG. 41 is a graph showing the frequency characteristic of reflectingattenuation of transmitted noise in comparative Example 11.

FIG. 42 is a graph showing the frequency characteristic of power loss oftransmitted noise in comparative Example 11.

FIG. 43 is a graph showing the level of internal coupling of noiseradiated from the electromagnetic noise suppressors of Examples 17, 18,19 and 20 and Comparative Examples 11 and 12, measured by a micro loopmethod.

FIG. 44 is a graph showing the level of internal coupling of noiseradiated from the electromagnetic noise suppressors of Examples 17, 18,19 and 20 and Comparative Examples 11 and 12, measured by a micro loopmethod.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail.

The electromagnetic noise suppressor of the present invention comprisesa base material containing a binding agent and a composite layer formedby integrating the binding agent that is a part of the base material anda magnetic material.

More specifically, as shown in high-resolution transmission electronmicroscope image of FIG. 1 and the sketch of FIG. 2 which simplifies theelectron microscope image, the electromagnetic noise suppressor 1comprises the base material 2 containing the binding agent and thecomposite layer 3 consisting of atoms of the magnetic material mixedwith molecules of the binding agent that is a part of the base material2.

<Composite Layer>

The composite layer 3 is, for example, a layer formed by physical vapordeposition of a magnetic material on the surface of the base material 2,where the magnetic material applied by physical vapor deposition isdispersed in the binding agent in the atomic state, without forming ahomogeneous film.

As shown in FIG. 2, the composite layer 3 consists of a portion wherevery small crystals of the magnetic material atoms disposed at a spacingof several angstroms in crystal lattice 4 is observed, a portion whereonly the binding agent 6 is observed without the magnetic material in avery small region, and a portion where atoms of the magnetic material 5are dispersed without crystallizing in the binding agent. Thus it isconsidered that the magnetic material and the binding agent areintegrated in a complex heterogeneous structure on the nanometer scale,without any grain boundary that shows the presence of fine particles ofthe magnetic material in crystal structure.

The thickness of the composite layer 3 is the depth of infiltration ofthe atoms of the magnetic material into the surface layer of the basematerial 2, that is dependent on such factors as the weight of themagnetic material deposited, kind of the binding agent and theconditions of physical vapor deposition, and is roughly in a range from1.5 to 3 times the thickness of the magnetic material layer formed bythe vapor deposition. The thickness of the magnetic material layerformed by the vapor deposition means the thickness of the layer formedby the vapor deposition of the magnetic material on a hard base materialthat does not allow infiltration of the atoms of the magnetic material.

The thickness of the composite layer 3 can be determined from the imageof a cross section taken by a transmission electron microscope or ascanning electron microscope (SEM). An SEM image of a cross section ofthe base material with a magnetic material layer formed by physicalvapor deposition is shown in FIG. 3. This shows the cross section of thebase material, excluding protrusions on the surface that will bedescribed later, where the composite layer (white horizontal line at thecenter) having a thickness of 40 nm (0.04 μm) is formed by vapordeposition of the magnetic material in a amount equivalent to 30 nm inthickness onto an elastic material containing about 45% by weight ofinorganic filler such as wet silica.

By forming the composite layer 3 with thickness of 0.005 μm or more,atoms of the magnetic material can be dispersed in the binding agent andintegrated therewith, supposedly providing a large loss characteristicin high-frequency region due to morphological anisotropy, thus achievingsufficient electromagnetic noise suppressing effect. When the thicknessof the composite layer exceeds 20 μm, on the other hand, a clearcrystalline structure and then a homogeneous film of the magneticmaterial is formed to become a bulk magnetic material. This leads to adecrease in morphological anisotropy and less electromagnetic noisesuppressing effect. Therefore, thickness of the composite layer 3 ispreferably 3 μm or less, more preferably 1 μm or less, and mostpreferably 0.3 μm or less.

When the magnetic material is deposited so as to form a homogeneousfilm, eddy currents are generated because of the low resistivity of themagnetic material, resulting in diminishing electromagnetic noisesuppressing effect of the magnetic material while reflecting functionbecoming dominant instead. Thus the film reflects electromagnetic noisegenerated by electronic circuits and components, instead of suppressingit, thus causing adverse effect on the electronic circuits. Therefore,homogeneous magnetic material film should not be formed during physicalvapor deposition of the magnetic material on the base material 2.Surface resistivity (D.C. resistivity) of the composite layer 3 ispreferably in a range from about 1×10¹ to 1×10¹⁰ Ω/□.

<Base Material>

(Binding Agent)

Examples of the binding agent that is the main component of the basematerial 2 include, but are not limited to, organic materials, forexample, resins such as polyolefine resin, polyamide resin, polyesterresin, polyether resin, polyketone resin, polyimide resin, polyurethaneresin, polysiloxane resin, phenol resin, epoxy resin, acrylic resin andpolyacrylate resin; diene rubbers such as natural rubber, isoprenerubber, butadiene rubber and styrene butadiene rubber; non-diene rubberssuch as butyl rubber, ethylene propylene rubber, urethane rubber andsilicone rubber. The binding agent may also be of thermoplastic orthermosetting in nature, or a material that has not yet cured. The resinor rubber described above that is modified, mixed or copolymerized mayalso be used.

The binding agent may also be an inorganic material that has a lowelastic modulus in shear that will be described later, such as an aerogel or foamed silica that has high void ratio and such a level ofhardness that can capture fine particles. It may also be used in theform of composite material with the organic material described above.

The binding agent preferably has a low elastic modulus in shear in viewof the ease of atoms of the magnetic material infiltrating into thebinding agent during the physical vapor deposition of the magneticmaterial. The elastic modulus in shear is preferably in a range from1×10⁴ to 1×10¹⁰ Pa, and more preferably in a range from 1×10⁴ to 5×10⁷Pa. The elastic modulus in shear is measured at the normal temperatureaccording to a procedure specified in JIS K 6254. A desirable value ofelastic modulus in shear may be obtained by heating the binding agent toa temperature of 100 to 300° C., although the temperature must becontrolled so as not to decompose or vaporize the material. Whenphysical vapor deposition is carried out at the normal temperature, thebinding agent is preferably an elastic material having hardness of about80° (JIS-A).

When elastic modulus in shear of the binding agent is low, atoms of themagnetic material are more likely to be dispersed in the surface layerof the base material due to infiltration of the atoms of the magneticmaterial into the base material 2 or deformation and fluidization of thebinding agent caused by collision of the atoms of the magnetic materialduring the physical vapor deposition of the magnetic material onto thebase material 2.

FIG. 4 is a laser microscope image of the surface of the base materialcoated with magnetic material by vapor deposition, showing the presenceof bumps and recesses on the surface. FIG. 5 shows the measurement ofsurface roughness, indicating that the bumps are about 6 μm in height.FIG. 6 that is a laser microscope image of the surface of the basematerial before vapor deposition, on the other hand, shows that thesurface before vapor deposition is flat. FIG. 7 shows the measurement ofcross section, indicating that mean surface roughness is 0.05 μm. FromFIGS. 4 to 7, it can be seen that vapor deposition resulted indeformation or fluidization of the base material.

It is preferable that the binding agent have high elastic modulus inshear after physical vapor deposition of the magnetic material, in orderto maintain the heterogeneous structure described previously. Byprocessing the binding agent to have a high elastic modulus in shearafter physical vapor deposition of the magnetic material, it is madepossible to surely prevent the atoms of the magnetic material orclusters thereof from coagulating and crystallizing into fine particleson the nanometer scale. Specifically, elastic modulus in shear ispreferably in a range from 1×10⁷ Pa or higher in a temperature range inwhich the electromagnetic noise suppressor is used. It is preferable tocrosslink the binding agent after physical vapor deposition of themagnetic material, in order to obtain the desired value of elasticmodulus in shear.

In this regard, the binding agent is preferably a thermosetting resin ora resin that is cured when exposed to an energy beam (ultraviolet light,electron beam) which allows the elastic modulus to below during vapordeposition and can be increased by crosslinking after the vapordeposition.

Size of the gap between molecules through which the atoms of themagnetic material can penetrate may be represented by gas permeability.While it is ideal to evaluate the gap between molecules of the bindingagent by using the permeability of argon gas or krypton gas of whichatom has a size comparable to that of the magnetic material, these gasesare not commonly used in the measurement of gas permeability. Therefore,permeability of carbon dioxide may be used instead. Resins that havehigh values of permeability to carbon dioxide gas at the normaltemperature include polyphenylene oxide, polymethylpentene, nylon 11,mixture or copolymer of high-impact polystyrene or other rubbercomponent and other component having carbon dioxide gas permeability of1×10⁻⁹ [cm³ (STP) cm/(cm²×s×cmHg)] or higher, or polybutadiene,polyisoprene, styrene butadiene rubber or silicone rubber having carbondioxide gas permeability of 1×10⁻⁸ [cm³ (STP) cm/(cm²×s×cmHg)] orhigher. Among these, rubbers such as silicone rubber are particularlypreferable in view of the elastic modulus in shear.

In order to prevent oxidization of the magnetic material, the bindingagent is preferably a resin that has low permeability to oxygen, such aspolyethylene, poly-trifluorochloroethylene or polymethyl methacrylatehaving oxygen permeability of 1×10⁻¹⁰ [cm³ (STP) cm/(cm²×s×cmHg)] orlower, or polystyrene terephthalate or polyacrylonitrile having oxygenpermeability of 1×10⁻¹² [cm³ (STP) cm/(cm²×s×cmHg)] or lower.

The binding agent may also contain silane coupling agent, titanatecoupling agent, nonionic surfactant, polar resin oligomer or the like,so that part of the magnetic material that has been turned into plasmaor ionized can react with the binding agent and be stabilized. Addingsuch an additive enables it to not only prevent oxidization but alsoprevent a homogeneous film from being formed by the coagulation of atomsso as to prevent the reflection of electromagnetic radiation by thehomogeneous film, thereby improving the absorbing property.

It is also preferable to process the surface of the base material 2 soas to add unevenness to the surface. Mean surface roughness ispreferably in a range from about 0.5 to 10 μm. While there is norestriction on the method of adding unevenness to the surface, sandblasting, etching or transfer of a rough surface may be employed.

The base material is preferably a foamed material since it containsvoids. The foamed material preferably has such a structure that isconstituted from fine cells and continuous voids and does not have askin layer on the surface. Cell size is about 100 μm or less, andpreferably 50 μm or less. Void ratio is preferably in a range from 5 to50%.

(Non-Halogen, Non-Antimony Flame Retarding Agent)

The base material 2 may contain non-halogen, non-antimony flameretarding agent added thereto in order to give flame retarding propertyto the electromagnetic noise suppressor of the present invention.

It is essential that the flame retarding agent not contain halogenelement or antimony. Compounds that contain a halogen element orantimony are regarded as imposing a load on the environment, and it isinevitable that commercial products not contain a halogen element orantimony.

However, non-halogen material cannot be regarded as being completelyfree of halogen elements. It is because chlorine exists in the naturalenvironment and also the material synthesizing process uses halogencompounds such as epichlorohydrin in the case of synthesis of epoxyresin, halogen element remains in the product material even when it hasbeen refined, which is very difficult to remove completely. According tothe present invention, therefore, a material is defined as halogen-freewhen the contents of chlorine and bromine therein are both not higherthan 0.09% as measured in accordance to the halogen-free copper-cladplate test method (JPCA-ES-01) of the JPCA Standards.

The non-halogen, non-antimony flame retarding agent may be one of knownmaterials, either in liquid or solid phase. Selection of thenon-halogen, non-antimony flame retarding agent is based on the kind ofresin or rubber that is used as the binding agent. For example,phosphorus-based flame retarding agent, nitrogen-based flame retardingagent, metal hydroxide, metal oxide, silicone-based flame retardingagent or platinum compound may be used as the non-halogen, non-antimonyflame retarding agent.

Phosphorus-based flame retarding agents include triphenyl phosphate,tricresyl phosphate, trixylenyl phosphate, triethyl phosphate,cresylphenyl phosphate, xylenyl-diphenyl phosphate,cresyl(di-2,6-xylenyl) phosphate, 2-ethylhexyl-diphenyl phosphate,dimethylmethyl phosphate, red phosphorus, yellow phosphorus, etc.

Nitrogen-based flame retarding agents include guanidine-based flameretarding agents such as guanidine sulfaminate, guanidine phosphate;urea-granyl-based flame retarding agents such as urea-granyl phosphate;melamine-based flame retarding agent such as melamine sulfate andpoly-melamine phosphate.

A phosphazene-based flame retarding agent that is a compound ofphosphorus and nitrogen and has a double bond may also be used. Thephosphazene compounds such as propoxyphosphazene, phenoxyphosphazene oraminophosphazene may be used as the phosphazene-based flame retardingagent.

As the metal hydroxide, aluminum hydroxide, magnesium hydroxide,dolomite, hydrotalcite, calcium hydroxide, barium hydroxide, zirconiumhydroxide, hydrate of tin oxide, etc. may be used. Other inorganic flameretarding agents include metal powder such as aluminum, iron, titanium,manganese, zinc, molybdenum, cobalt, bismuth, chromium, nickel, copper,tungsten or tin, metal oxide such as silica, aluminum oxide, iron oxide,titanium oxide, manganese oxide, magnesium oxide, zirconium oxide, zincoxide, molybdenum oxide, cobalt oxide, bismuth oxide, chromium oxide,tin oxide, nickel oxide, copper oxide or tungsten oxide, and compoundsuch as zinc borate, zinc metaborate, barium metaborate, zinc carbonate,magnesium carbonate, calcium carbonate or barium carbonate.

As the silicone-based flame retarding agent, silicone powder having anepoxy group or a methacryl group may be used.

As the platinum compound, platinum hexachlorate (IV), dinitrodiamineplatinum (II), tetramine dichloroplatinum (II), etc., may be used.

As the flame retarding agent, besides the so-called additive flameretarding agent that is simply added to the binding agent, such areactive flame retarding agent may also be used that reacts with theskeleton of the binding agent and introduces into the binding agent acompound that includes flame retarding elements such as nitrogen orphosphorus.

Flame retarding agents are divided into a type that resists flames and atype that resists glowing, and it is effective to use flame retardingagents in combination of a plurality of types in accordance to theapplication. Since a flame retarding agent may compromise otherproperties of the electromagnetic noise suppressor while making theelectromagnetic noise suppressor difficult to burn, type and amount ofthe flame retarding agent must be set for proper trade-off of theproperties.

The amount of the non-halogen, non-antimony flame retarding agent to beadded varies depending on the types of the binding agent and the flameretarding agent. In the case of the phosphorus-based flame retardingagent, for example, 0.5 to 20 parts by weight of the flame retardingagent is preferably added for 100 parts by weight of the binding agent.In the case of metal hydroxide, 50 to 300 parts by weight of the flameretarding agent is preferably added for 100 parts by weight of thebinding agent. In the case of the platinum compound, for example, 0.01to 1 part by weight of the flame retarding agent is preferably added for100 parts by weight of the binding agent. When the amount ofnon-halogen, non-antimony flame retarding agent is insufficient,sufficient flame retarding property may not be given to theelectromagnetic noise suppressor. When excessive amount of non-halogen,non-antimony flame retarding agent is added, desired level of elasticmodulus in shear of the binding agent may not be obtained and at leastone of the mechanical strength of the binding agent, such as tearstrength and tensile strength may decrease.

The electromagnetic noise suppressor shows sufficient flame retardingproperty when the base material 2 thereof includes the non-halogen,non-antimony flame retarding agent. Since the magnetic material isintegrated with the binding agent at the atom level in the compositelayer 3, it is made possible to suppress such a problem as theelectromagnetic noise suppressor becomes easier to burn due to thecatalyst effect or increase in thermal conductivity due to the magneticmaterial powder with decreasing self-extinguishing performance as in thecase of the electromagnetic noise suppressor containing the conventionalmagnetic material powder dispersed in the binding agent. As a result,the amount of the non-halogen, non-antimony flame retarding agent can besignificantly reduced in comparison to the conventional electromagneticnoise suppressor.

(Electrically Conductive Filler)

An electrically conductive filler may be added to the base material 2 inorder to give shielding property as the electromagnetic noise reflectingeffect to the electromagnetic noise suppressor of the present invention.The electromagnetic noise suppressor 10 shown in FIG. 8 includes asupport layer 8, the base material 2 stacked on the support layer 8 andthe composite layer 3 where atoms of the magnetic material are mixedwith a part of the base material 2. In the base material 2, a dielectricmaterial powder 11 and the electrically conductive filler 12 aredispersed in the binding agent 6.

The electrically conductive filler 12 is preferably an electricallyconductive powder of at least one type selected from a group consistingof metal powder, metal fiber, metal-coated fine particles, fine carbonparticles and carbon nano-tube, in order to further improve theshielding property.

While the shape of the electrically conductive filler 12 variesdepending on the kind of material, it may be metal particles ofindefinite shape, needle shaped such as carbon nano-tubes or astructured sphere of carbon, and there is no restriction on the shape aslong as the material increases electrical conductivity when added. Sizeof the electrically conductive filler 12 is preferably 10 μm or less inthe case of particles or indefinite shape, or 5 μm or less in fiberdiameter in the case of fibers. Larger size increases the thickness ofthe base material 2 and makes it difficult to make a thin product.

The amount of the electrically conductive filler 12 dispersed in thebase material is preferably from 10 to 50% by volume of the basematerial 2 (100% by volume). When the content is less than 10% byvolume, it becomes difficult to stably achieve electrical conductivityand, when the content exceeds 50% by volume, elastic modulus in shear ofthe base material 2 becomes so high that it is difficult to form thecomposite layer 3 through integration with the magnetic material.

Intrinsic volume resistivity (may also be referred to as intrinsicresistivity) of the base material 2 containing the electricallyconductive filler 12 is preferably 500 Ω□cm or less as measuredaccording to JIS K 7194, and more preferably 50 Ω□cm or less.

In the electromagnetic noise suppressor shown in FIG. 8, the compositelayer 3 suppresses the noise generated by electronic components andcircuits, the electrically conductive filler 12 dispersed in the basematerial 2 shields the noise generated from the substrate or othercomponent outside of the electronic components and suppresses theelectromagnetic coupling from increasing due to reflection ofunnecessary electromagnetic radiation.

(Dielectric Material Powder)

An electrically conductive powder 11 may be contained in the basematerial 2 in order suppress the reflection of unnecessaryelectromagnetic radiation.

The electrically conductive powder 11 is preferably such a material thathas high dielectric constant in high-frequency region, and relativelyflat frequency characteristic of the dielectric constant. Since additionof the electrically conductive powder 11 achieves impedance matchingwith the space, reflection of unnecessary electromagnetic radiationbecomes less likely to occur.

It is preferable to use at least one kind of dielectric material powderselected from a group consisting of barium titanate-based ceramic,zirconium titanate-based ceramic and lead provskite-based ceramic forthe electrically conductive powder 11, in order to prevent thereflection of unnecessary electromagnetic radiation becomes fromoccurring.

While there is no restriction on the particle shape of the dielectricmaterial powder 11, substantially spherical particles are preferred.Particle size of the dielectric material powder 11 is preferably 5 μm orless. When larger than 5 μm, the dielectric material powder 11 cannot bedispersed in the base material and it becomes difficult to make a thinproduct. Particle size is more preferably 1 μm or less.

The amount of the dielectric material powder 11 to be added ispreferably from 5 to 50% by volume of the base material 2 (100% byvolume). When the content is less than 5% by volume, the effect ofdielectric loss in high-frequency region cannot be achieved. When thecontent exceeds 50% by volume, elastic modulus in shear of the basematerial 2 becomes so high that it is difficult to form the compositelayer 3 through integration with the magnetic material.

In the case in which both the dielectric material powder 11 and theelectrically conductive filler 12 are added together, they may be addedin such quantities that achieve the respective effects, but the totalamount of the dielectric material powder 11 and the electricallyconductive filler 12 is preferably not more than 50% by volume of thebase material 2 (100% by volume). When the total amount exceeds 50% byvolume, elastic modulus in shear of the base material 2 becomes so highthat it is difficult to form the composite layer 3 through integrationwith the magnetic material.

(Other Additives)

In addition to the above, the binding agent may also containreinforcement fillers, dispersants, anti-aging agents, anti-oxidizingagents, colorants, thixotropy enhancing agents, plasticizers,lubricants, antistatic agents, heat resistance enhancing agents andultraviolet absorbents. Care should be exercised, however, since addinga hard material leads to collision with the atoms of the magneticmaterial, thus resulting in insufficient dispersion. substituent mayalso be improved by coating with silicon oxide or silicon nitride byvapor deposition, after the vapor deposition of the magnetic material.

<Support Layer>

In the case in which the base material 2 is difficult to handle due tosmall thickness or elastic modulus in shear in the operating temperaturerange, the support layer 8 may be provided as shown in FIG. 9. Thesupport layer 8 may be either made of a material similar to that of thebase material 2, or metal foil or ceramic foil that has flexibility. Itis preferable that rigidity of the support layer 8 be higher than thatof the binding agent 6 that constitutes the base material 2, and elasticmodulus in shear be higher. It is desirable that the support layer 8 bethin, of which thickness is preferably 50 μm or less, more preferably 25μm or less.

<Heat Conduction Layer>

The electromagnetic noise suppressor of the present invention may beprovided with a heat conduction layer so as to have heat dissipatingproperty.

The heat conduction layer is, for example, a sheet containing thermallyconductive filler. The thermally conductive filler may be a metal suchas copper or aluminum, a low-melting point alloy of such metals asaluminum or indium, metal oxide such as alumina, silica, magnesia, redoxide, beryllia or titania, metal nitride such as aluminum nitride,silicon nitride or boron nitride, or a compound such as silicon carbide,but is not limited to these materials.

Mean particle size of the thermally conductive filler is preferably in arange from 0.1 to 100 μm, and more preferably from 1 to 50 μm. When meanparticle size is less than 0.1 μm, specific surface area of theparticles becomes too large and it becomes difficult to fill with highdensity. When mean particle size exceeds 100 μm, the heat conductionlayer may have finely roughened surface, resulting in resistance to heattransmission through contact.

Content of the thermally conductive filler is preferably in a range from10 to 85% by volume, depending on the kind of filler. When the contentis less than 10% by volume, required level of heat conductivity may notbe obtained. When the content exceeds 85% by volume, the sheet maybecome very brittle.

While there is no restriction on the material that makes the heatconduction layer, silicone rubber, urethane rubber or the like ispreferably used for the reason of heat resistance and weatherability.The electromagnetic noise suppressor having the heat conduction layer isparticularly useful for the application of dissipating heat fromsemiconductor that generates much heat such as power transistors orthyristors.

<Flame Retarding Resin Layer>

The electromagnetic noise suppressor of the present invention may beprovided with a flame retarding resin layer so as to have flameretarding property.

The electromagnetic noise suppressor having the flame retarding resinlayer may be formed as an electromagnetic noise suppressor 20 thatcomprises the flame retarding resin layer 7, the base material 2 that isstacked on the flame retarding resin layer 7 and the composite layer 3consisting of atoms of the magnetic material mixed with molecules of thebinding agent that is a part of the base material 2, as shown in FIG.10. It may also be formed as an electromagnetic noise suppressor 21 thatcomprises the base material 2, the composite layer 3 consisting of atomsof the magnetic material mixed with molecules of the binding agent thatis a part of the base material 2 and the flame retarding resin layer 7that is stacked on the surface of the composite layer 3, as shown inFIG. 11, or an electromagnetic noise suppressor 22 that comprises theflame retarding resin layer 7, the base material 2 stacked on thesurface thereof, the composite layer 3 consisting of atoms of themagnetic material mixed with molecules of the binding agent that is apart of the base material 2 and the flame retarding resin layer 7 thatis stacked on the surface of the composite layer 3, as shown in FIG. 12.

The flame retarding resin layer 7 is formed from a flame retarding resinlayer. The flame retarding resin layer is a resin that is hard to igniteand, even when ignited, extinguishes in a short time.

As the flame retarding resin layer, resins that have high decompositiontemperatures and do not generate much combustible material whendecomposed, or that have high critical oxygen indices may be used.Specifically, fluororesin, polyimide resin, polyamideimide resin,polyethersulfone resin, polyether-etherketone resin, polyether-imideresin, polyphenylene sulfide resin or liquid crystal polymer may beused. The flame retarding resin layer preferably has flame retardingproperty of UL94 VTM-0, VTM-1 or UL94 V-0, V-1.

Even a resin that is poor in flame retarding property may be used as theflame retarding resin layer of the present invention, if it acquiresflame retarding property of UL94 VTM-0, VTM-1 or UL94 V-0, V-1 by addinga flame retarding agent or combining with a flame retarding resin layer.However, it is desirable that a flame retarding agent based on halogenor antimony that imposes a load on the environment is not be used.

The flame retarding resin layer may contain reinforcement fillers, flameretarding agents, auxiliary flame retarding agents, anti-aging agents,anti-oxidizing agents, colorants, plasticizers, lubricants, heatresistance enhancing agents or the like.

While there is no limitation to the thickness of the flame retardingresin layer 7, it is preferably thin in order to produce a thin andcompact electromagnetic noise suppressor. Specifically, the thickness ispreferably 50 μm or less, more preferably 25 μm or less.

Since the electromagnetic noise suppressor of the present invention hassuch a constitution as the magnetic material is integrated with thebinding agent at the atomic level in the composite layer 3, it is madepossible to suppress problems such as the electromagnetic noisesuppressor becoming easier to burn due to the catalyst effect or an dueto increase in thermal conductivity caused by the magnetic materialpowder with decreasing self-extinguishing performance as in the case ofthe electromagnetic noise suppressor containing the conventionalmagnetic material powder dispersed in the binding agent. As a result,the electromagnetic noise suppressor of the present invention isrendered sufficient flame retarding property by simply providing theflame retarding resin layer 7.

(Electrically Conductive Layer)

An electrically conductive layer may be provided to the electromagneticnoise suppressor of the present invention in order to give shieldingproperty for reflecting electromagnetic noise.

The electromagnetic noise suppressor 30 shown in FIG. 13 comprises anelectrically conductive layer 9, the base material 2 stacked on theelectrically conductive layer 9 consisting of the dielectric materialpowder 11 dispersed in the binding agent 6 and the composite layer 3where atoms of the magnetic material are mixed with a part of the basematerial 2. In this example, the electrically conductive layer 9 isconstituted from an electrically conductive film comprising a supportfilm 13 and a metal layer 14 formed by physical deposition of metal onthe support film 13.

In the electromagnetic noise suppressor 31 shown in FIG. 14, the basematerial 2 consisting of the dielectric material powder 11 dispersed inthe binding agent 6 is provided on both sides of the electricallyconductive layer 9 that consists of the dielectric material powder 11having the support film 13 and the metal layer 14, and the compositelayer 3 is provided on the surface of the base material 2.

In the electromagnetic noise suppressor 32 shown in FIG. 15, the basematerial 2 consisting of the dielectric material powder 11 dispersed inthe binding agent 6 and the composite layer 3 are provided in pluralityon one side of the electrically conductive layer 9 that consists of thesupport film 13 and the metal layer 14.

In the electromagnetic noise suppressor 30 shown in FIG. 13, onecomposite layer 3 is provided via the base material 2 on one side of theelectrically conductive layer 9, although the composite layers 3 may beprovided via the base material 2 on both sides of the electricallyconductive layer 9 as shown in FIG. 14, or a plurality of the compositelayers 3 may be provided via the base material 2 on one side of theelectrically conductive layer 9 as shown in FIG. 15, in theelectromagnetic noise suppressor of the present invention. In theaspects shown in FIGS. 13 and 15, the metal layer 14 may be providedeither on the side of the electrically conductive layer 9 opposite tothe base material 2 or on the base material 2 side. The metal layer 14is preferably provided on the base material 2 side in order to protectthe thin metal layer 14 in packaged condition.

The electromagnetic noise suppressor 33 shown in FIG. 16 is an exampleof an aspect where the electrically conductive layer 9 is made byinterlacing of metal on the surface of which the base material 2consisting of the dielectric material powder 11 dispersed in the bindingagent 6 is provided and the composite layer 3 is provided where atoms ofthe magnetic material are mixed with a part of the base material 2.

Intrinsic volume resistivity of the electrically conductive layer 9 ispreferably 500 Ω□cm or less as measured according to JIS K 7194, andmore preferably 50 Ω□cm or less.

The electrically conductive layer 9 is preferably selected from a groupconsisting of metal foil, fabric of metal fibers, fabric of electricallyconductive fibers, interlaced metal wires, interlaced electricallyconductive fibers, organic polymer layer containing an electricallyconductive filling agent dispersed therein and electrically conductivefilm.

The metal foil may be made of aluminum, nickel, tin, copper, phosphorbronze, nickel silver, brass or other copper alloy. The fabric of metalfibers may be, for example, made of nickel or stainless steel fibers.The fabric of electrically conductive fibers may be, for example, anonwoven fabric of carbon fibers or polyester fibers coated with copperand nickel in two layers of plating. The interlaced electricallyconductive fibers may be a mesh of nickel, tin, copper, phosphor bronze,nickel silver, brass or other copper alloy. The interlaced electricallyconductive fibers may be, for example, a mesh of fibers plated withcopper, nickel or other metal.

The electrically conductive layer 9 may be an organic polymer layerhaving electrically conductive filler dispersed therein. While there isno restriction on the organic polymer, it may be an insulating organicpolymer. The organic polymer used in the electrically conductive layermay be, for example, resin such as polyolefine, polyester,polyether[polyketone, polyurethane or the like, or elastomer such assilicone, isoprene, butadiene, styrene butadiene, urethane or ethylenepropylene. The electrically conductive filler used in the electricallyconductive layer may be metal particles, carbon fiber, carbonnano-tubes, fine carbon particles or the like.

The electrically conductive film may be, for example, one that consistsof the support film 13 and the metal layer 14. In the case in which theelectrically conductive film including the support film 13 and the metallayer 14 is used as the electrically conductive layer 9, thickness ofthe metal layer 14 is preferably in a range from 5 to 500 nm. When thethickness is less than 5 nm, electrical conductivity of the metal layerbecomes unstable and may not be able to provide electromagneticradiation shielding effect. Thickness exceeding 500 nm makes iteconomically disadvantageous. Thickness in a range from 5 to 150 nm ispreferable in order to make the electromagnetic noise suppressor 30lighter in weight, smaller in thickness and flexible.

The support film 13 may be made of, for example, a resin such aspolyolefine, polyester, polyether, polyketone, polyurethane or the like,or an elastomer such as silicone, isoprene, butadiene, styrenebutadiene, urethane or ethylene propylene. A flexible film such aspolyimide film or polyester film may also be used.

The metal layer 14 may be formed by plating the support film 13 with ametal, laminating a metal foil on the support film 13, or physical vapordeposition of a metal on the support film 13. Among these, physicalvapor deposition of a metal on the support film 13 makes it possible toobtain the metal layer 14 that satisfies the requirement of thicknessfrom 5 to 500 nm and is uniform.

In the plating process, a metal such as nickel, tin, copper, phosphorbronze, nickel silver, brass or other copper alloy may be used. In thelamination process, a foil made of aluminum, copper or nickel may beused.

The physical vapor deposition of a metal to obtain the metal layer 14 ispreferably carried out by opposing target type magnetron sputteringprocess. The opposing target type magnetron sputtering process, which isa dry process, does not require disposal of waste liquid and is saferand more favorable with regards to the environment than the platingprocess, which is a wet process that uses a plating liquid, and isregarded as a better process that can form the metal layer from uniformthin film while easily adjusting the film thickness with highproductivity.

In the electromagnetic noise suppressor that has the electricallyconductive layer 9, the composite layer 3 suppresses the noise generatedby electronic components and circuits, and the electrically conductivelayer 9 shields the noise generated from the substrate or othercomponent outside of the electronic components and suppresses theelectromagnetic coupling from increasing due to reflection ofunnecessary electromagnetic radiation.

(Electromagnetic Noise Suppressor)

In the case in which the magnetic material has a size on the order ofmicrometers, it is necessary to use a large amount of the magneticmaterial with a high density and use thick and heavy electromagneticnoise suppressor in order to achieve high transmission absorbing rate.In the case in which the magnetic material having a size on the order ofnanometers is integrated with the binding agent to form a complicatedheterogeneous structure, a property different from the case of using themagnetic material on the order of micrometers is obtained, thusresulting in higher magnetic permeability and broader frequency band ofabsorption. Thus, it becomes unnecessary to use a large amount of themagnetic material with a high density and use thick and heavyelectromagnetic noise suppressor in order to achieve a high transmissionabsorbing rate as in the above case.

Although it is difficult to directly observe the state of the magneticmaterial in the composite layer 3, it can be determined that thecomposite layer 3 has a complicated heterogeneous structure where themagnetic material having a size on the order of nanometers is integratedwith the binding agent, by measuring the maximum transmissionattenuation of electromagnetic radiation (dB/μm) per unit thickness ofthe composite layer 3 of the electromagnetic noise suppressor.

When maximum transmission attenuation of electromagnetic radiation perunit thickness of the composite layer 3 is in a range from −0.5 to −500dB/μm, it is indicated that the magnetic material having a size on theorder of nanometers is integrated with the binding agent. According tothe present invention, it is necessary that maximum transmissionattenuation of electromagnetic radiation per unit thickness of thecomposite layer 3 be in a range from −0.5 to −500 dB/μm. When this indexis lower than −0.5 dB/μm (for example, −0.4 dB/μm) or higher than −500dB/μm (for example, −600 dB/μm), the effect of suppressingelectromagnetic noise or it becoming necessary to increase the thicknessof the electromagnetic noise suppressor in order to obtain the desiredeffect of suppressing electromagnetic noise, thus resulting in limitedspace available for the electronic devices.

Maximum transmission attenuation of electromagnetic radiation refers tothe maximum attenuation of transmission measured in the frequency bandin which it is desired to suppress the electromagnetic noise. It isdetermined by measuring the electromagnetic radiation transmittedthrough the composite layer 3 while changing the frequency in bands suchas from 10 MHz to 1 GHz, from 100 MHz to 3 GHz, from 1 to 3 GHz, from 3to 20 GHz, from 20 to 50 GHz and 50 to 100 GHz, and taking theelectromagnetic radiation transmission attenuation at the frequencywhere the electromagnetic radiation is attenuated most. The maximumtransmission attenuation of electromagnetic radiation is −11.9 dB at 3.0GHz where the curve of the electromagnetic radiation transmissionattenuation (thick line) shows the lowest level in the graph shown inFIG. 21, −30.2 dB at 8.0 GHz where the curve of the electromagneticradiation transmission attenuation (thick line) shows the lowest levelin the graph shown in FIG. 22 and −32.9 dB at 15.7 GHz where the curveof the electromagnetic radiation transmission attenuation (thick line)shows the lowest level in the graph shown in FIG. 23.

Even when the electromagnetic radiation transmitted through thecomposite layer 3 is weak, it must have a practical value for theapplication, and it is necessary that the attenuation be in a range from−6 to −50 dB which is regarded as effective in suppressing theelectromagnetic noise, and in a range from −10 to −50 dB at the peak.

Similarly, reflection of the electromagnetic radiation is preferably lowin order to achieve electromagnetic noise suppressing effect, andreflection attenuation in a frequency band where transmissionattenuation shows the maximum value is preferably in a range from −6 to−50 dB and more preferably from −10 to −50 dB.

The electromagnetic noise suppressor of the present invention canachieve a high power loss that represents the electromagnetic noisesuppressing effect, supposedly because vapor deposition of a smallamount of magnetic material onto the base material affects the quantumeffect of granular particles of nanometer scale, magnetic anisotropy ofthe material, magnetic morphological anisotropy or anisotropy due toexternal magnetic field, although theoretical explanation has not beenpresented.

The power loss can be determined by measuring the changes in S11(reflection characteristic) and S21 (transmission characteristic) asshown in FIG. 33 and calculating by the following formula from thevalues of S11 and S22 at a particular frequency. Values of power lossfall within a range from 0 to 1.Power loss (Ploss/Pin)=1−(|Γ|² +|T| ²)S11=20 log|Γ|S21=20 log|T|

Where Γ is the reflection coefficient and T is the transmissioncoefficient.

Power loss is a comprehensive index of reflection and transmissioncharacteristics of electromagnetic noise suppressing function, and it isrequired that reflection attenuation and transmission attenuation havepractical values. Thus the electromagnetic noise suppressor of thepresent invention preferably has power loss at 1 GHz in a range from 0.3to 0.65, more preferably from 0.4 to 0.65.

In order for the electromagnetic noise suppressor to functionsufficiently, it is preferable that the reflection attenuation be largerthan transmission attenuation while reflection attenuation is not lessthan −6 dB and transmission attenuation is not less than −3 dB (forexample, reflection attenuation is −7 dB and transmission attenuation is−4 dB), that is power loss is not less than 0.3. Smaller power losscannot be regarded as the result of sufficient electromagnetic noisesuppressing function. It is more preferable that reflection attenuationbe not less than −10 dB and transmission attenuation be not less than −3dB (for example, reflection attenuation is −11 dB and transmissionattenuation is −4 dB), that is power loss is not less than 0.4.Sufficient electromagnetic noise suppressing function can be achievedwhen both the reflection attenuation and the transmission attenuationare −10 dB or higher (for example, reflection attenuation is −12 dB andtransmission attenuation is −11 dB). While it is desired to obtain powerloss higher than 0.65 in view of better characteristics, it has not beenpossible to obtain power loss higher than 0.65 at 1 GHz with the presenttechnologies whatever selections are made with regards to the magneticmaterial contained in the electromagnetic noise suppressor and theconditions of vapor deposition onto the binding agent.

Power loss of the electromagnetic noise suppressor in a range from 0.3to 0.65 can be achieved by carrying out physical vapor deposition withhigh energy when forming the electromagnetic noise suppressor, andproperly selecting the conditions of vapor deposition, the amount of themagnetic material deposited and other factors so as to accomplish thestate that the binding agent and the magnetic material are integrated atthe nanometer level as the basic prerequisite.

As shown in FIGS. 30 to 32, power loss curve of the conventionalelectromagnetic noise suppressor is convex downward, in which the powerloss shows a relatively small increase with the frequency around 1 GHz,and shows larger increase beyond a frequency higher than 1 GHz, with aninflection point at a frequency higher than 1 GHz. Power loss curve ofthe electromagnetic noise suppressor of the present invention, incontrast, is convex upward in which the power loss shows a steepincrease in a frequency region from below 1 GHz to 1.5 GHz, then theincrease slows down beyond 1.5 GHz or 2 GHz, as shown in FIGS. 27 to 29.Thus the electromagnetic noise suppressor of the present invention hassufficient power loss at frequencies around 1 GHz where it is expectedto have practical effect.

The electromagnetic noise suppressor of the present invention contains asmall amount of the magnetic material that forms the composite layer 3.Therefore, increase in the specific gravity of the electromagnetic noisesuppressor is several percentage points at the most over that of thebase material that consists solely of binding agent. Consequently,specific gravity of the electromagnetic noise suppressor is from 0.9 to1.5 in the case in which a resin or rubber is used as the binding agent.As a result, satisfactory property and sufficient mechanical strength ofthe binding agent can be maintained since smaller amounts of themagnetic material is used than the case of the conventionalelectromagnetic noise suppressor.

The electromagnetic noise suppressor of the present invention may haveeither planar configuration such as a sheet or a three-dimensionalstructure. The shape may also be adapted to the shape of an article whenit is used to cover the surface of the article.

A plurality of electromagnetic noise suppressors each having a singlecomposite layer formed thereon may also be stacked one on another,thereby providing a plurality of composite layers. Total thickness ofthe stacked electromagnetic noise suppressors is preferably in a rangefrom about 20 to 200 μm. It is preferable that the thickness of the basematerial be determined in accordance with the total thickness of theelectromagnetic noise suppressor.

In the stacked electromagnetic noise suppressor, the composite layers ofthe electromagnetic noise suppressors that constitute the individuallayers may be the same or different from each other.

In the electromagnetic noise suppressor, since some of theelectromagnetic radiation is reflected and may affect the electroniccircuits and components that emit the electromagnetic radiation,reflection can be suppressed by such a graded configuration as thethickness of the composite layers to be stacked is gradually increased,starting with the layer on the electronic component side.

<Method of Manufacturing Electromagnetic Noise Suppressor>

The method of manufacturing an electromagnetic noise suppressor will nowbe described.

The method of manufacturing the electromagnetic noise suppressor of thepresent invention includes a vapor deposition process where thecomposite layer is formed on the base material surface by physical vapordeposition of the magnetic material on the base material.

(Vapor Deposition Process)

First, general description of physical vapor deposition (PVD) will begiven.

In physical vapor deposition (PVD), a material is vaporized in a vacuumvessel and is deposited on a substrate that is placed in the vicinity ofthe vaporized material, so as to form a thin film. The process isdivided by the method of evaporation into vaporization process andsputtering process. Vaporization processes include EB vapor depositionand ion plating, and sputtering processes include high frequencysputtering, magnetron sputtering and opposing target type magnetronsputtering process.

In the EB vapor deposition, since the vapor particle has small energy of1 eV, less damage is caused to the substrate and the film tends tobecome porous and have insufficient strength, while the specificresistivity of the film increases.

In the ion plating process, since ions of argon gas and vaporizedparticles are accelerated and collide with the substrate, particleenergy is about 1 KeV, higher than in the case of EB. Therefore a filmhaving high adhesive force can be obtained, although it cannot beavoided that particles having sizes on the order micrometers, calleddroplets, are deposit on the surface and cause interrupt of thedischarge. An oxide film may be formed by introducing a reactive gassuch as oxygen.

In magnetron sputtering, although the target (material to be vaporized)is utilized with less efficiency, growth rate is higher since strongplasma is generated by the effect of magnetic field and a high energy ofseveral tens of electron volts (eV) is given to the particle. In thehigh frequency sputtering, an insulating target may be used.

Among the magnetron sputtering processes, the opposing target typemagnetron sputtering process is a process where plasma is generatedbetween opposing targets and is confined by the magnetic field, whilethe substrate is placed outside of the opposing targets so as to form adesired thin film without causing damage from the plasma. Therefore, afilm of the same composition as that of the target made of densematerial can be formed without need to sputter the thin film of thesubstrate again and mitigating the collision of the sputtered atoms withfurther higher growth rate.

While the magnetic flux passes through the target made of the magneticmaterial and therefore sputtering rate is determined by the thickness ofthe target or it becomes difficult to establish electric discharge inthe case of conventional magnetron sputtering, magnetic field isgenerated in the direction perpendicular to the target surface to besputtered in the case of opposing target type magnetron sputteringprocess so that the magnetic field is maintained even when a magneticmaterial is used as the target and sputtering can be carried out at ahigh rate regardless of the thickness of the target.

For the reasons described above, the opposing target type magnetronsputtering process is preferable among the various processes of physicalvapor deposition for manufacturing the electromagnetic noise suppressorof the present invention.

In the case in which the binding agent is a resin (or a rubber),covalent bonding energy of the resin is about 4 eV. Bonding energies ofC—C, C—H, Si—O and Si—C, for example, are 3.6 eV, 4.3 eV, 4.6 eV and 3.3eV, respectively. In the opposing target type magnetron sputteringprocess, in contrast, the vaporized particles have high energies andtherefore collide while breaking part of the chemical bonding of theresin.

Therefore, it is supposed that when the binding agent made of resin (orrubber) has a sufficiently low elastic modulus in the present invention,molecules of the resin vibrate and are sometimes broken when themagnetic material is deposited, resulting in localized mixing of theatoms of the magnetic material and the resin and interaction with theresin, so that the composite layer having a heterogeneous structure onthe scale of nanometers is formed.

It is preferable to apply the magnetic material with particle energy of5 eV or higher to the binding agent by physical vapor deposition sinceit enables it to disperse a large amount of the magnetic material in thebinding agent at the same time. Since a large amount of the magneticmaterial can be processed in a single deposition run, theelectromagnetic noise suppressor having high electromagnetic noisesuppressing effect can be easily made. Since velocity of the bindingagent in vibration thereof is lower than the velocity of the particle,rate of vapor deposition is preferably set to be slow in accordance tothe timing of relaxation of the binding agent, about 60 nm/min or lesswhile it depends on the kind of magnetic material.

As the magnetic material to be vaporized in the vapor depositionprocess, a metal-based soft magnetic material, an oxide-based softmagnetic material and/or a nitride-based soft magnetic material ismainly used. Either one of these materials or a mixture of two or moreof these materials may be used.

As the metal-based soft magnetic material, iron or an iron alloy iscommonly employed. As the iron alloy, Fe—Ni, Fe—Co, Fe—Cr, Fe—Si, Fe—Al,Fe—Cr—Si, Fe—Cr—Al, Fe—Al—Si or Fe—Pt alloy may be used. Either one ofthese materials or a mixture of two or more of these materials may beused. Besides iron and iron alloy, cobalt, nickel or an alloy thereofmay also be used. Nickel has resistance against oxidation and istherefore preferably used independently.

As the oxide-based soft magnetic material, ferrite is preferably used.Specifically, MnFe₂O₄, CoFe₂O₄, NiFe₂O₄, CuFe₂O₄, ZnFe₂O₄, MgFe₂O₄,Fe₃O₄, Cu—Zn-ferrite, Ni—Zn-ferrite, Mn—Zn-ferrite, Ba₂Co₂Fe₁₂O₂₂,Ba₂Ni₂Fe₁₂O₂₂, Ba₂Zn₂Fe₁₂O₂₂, Ba₂Mn₂Fe₁₂O₂₂ , Ba₂Mg₂Fe₁₂O₂₂,Ba₂Cu₂Fe₁₂O₂₂ or Ba₃Co₂Fe₂₄O₄₁, may be used. These variations of ferritemay be used either independently or in a combination of two more kindsthereof.

As nitride-based soft magnetic material, Fe₂N, Fe₃N, Fe₄N, Fe₁₆N₂, etc.are known. These nitride-based soft magnetic materials have highmagnetic permeability and high corrosion resistance, and are preferablyused.

During the physical vapor deposition of the magnetic material onto thebinding agent, since atoms of the magnetic material infiltrate thebinding agent in the form of plasma or ions, composition of the magneticmaterial dispersed in the binding agent is not necessarily the same asthat of the magnetic material before it is vaporized. The magneticmaterial may have reacted with part of the binding agent and changedinto paramagnetic material or antiferromagnetic material.

The amount of the magnetic material deposited on the binding agent in asingle deposition run is preferably 200 nm or less in terms of thicknessof the magnetic material layer. When deposited to larger thickness,limitation of the capacity of the binding agent to include the magneticmaterial is reached such that the magnetic material cannot be dispersedin the binding agent and is deposited on the surface, thereby forming acontinuous bulk film that has uniform conductivity. Therefore, theamount of the magnetic material to be deposited is preferably 100 nm orless, and more preferably 50 nm or less. In view of the electromagneticnoise suppressing effect, the amount of the magnetic material to bedeposited is preferably 0.5 nm or more.

Since less amount of deposition leads to lower electromagnetic noisesuppressing effect, the total amount of the magnetic material can beincreased by stacking a plurality of electromagnetic noise suppressorsthereby to provide a plurality of composite layers. The total amount ofdeposition is preferably in a range from 10 to 500 nm in terms of totalthickness of the magnetic material, while it depends on the requiredlevel of electromagnetic noise suppression. Part of the layers to bestacked may also be formed as bulk metal layers that have continuity, soas to have reflectivity to electromagnetic radiation. The layers mayalso be formed in composite structure with the dielectric material layerso as to control the electromagnetic noise suppressing effect.

The amount of deposition can be determined by measuring the thicknessthe magnetic material layer deposited on the hard substrate layer madeof glass or silicon.

While there is no restriction on the thickness of the binding agent usedin the vapor deposition process, it is preferably as small as possiblein order to make an electromagnetic noise suppressor compact.Specifically, the thickness is preferably 50 μm or less, and morepreferably 10 μm or less.

(Process to Fabricate Stack)

In the case in which the electromagnetic noise suppressor of the presentinvention has layers other than the base material and the compositelayer, such as a support layer, heat conduction layer, flame retardingresin layer or electrically conductive layer, the manufacturing processincludes a stack fabricating process where the stack having the basematerial that includes the binding material and other layers is made,and a vapor deposition process where the composite layer is formed onthe base material surface by physical vapor deposition of the magneticmaterial on the base material.

The stack can be formed by, for example, exclusion lamination of thebinding agent onto various films that constitute other layers;application of the binding agent to the various films; and lamination ofbase material film containing the binding agent and various films bymeans of adhesive agent or the like.

<Article with Electromagnetic Noise Suppressing Function>

The article with an electromagnetic noise suppressing function of thepresent invention is an article of which surface is at least partlycovered by the electromagnetic noise suppressor of the presentinvention.

The article may be an electronic component, a printed wiring board whereelectronic components are mounted, electric connector, flat cable, keytop member for pushbutton switch, insert sheet for preform,semiconductor integrated circuit, etc.

Specific examples of the article with an electromagnetic noisesuppressing function of the present invention will be described below.

(Electronic Component)

The electromagnetic noise suppressor of the present invention is capableof suppressing electromagnetic radiation generated by electroniccomponents of various electoronic apparatuses. Specifically, among theelectronic components mounted on an electoronic apparatus, those whichmay malfunction under the influence of incoming electromagnetic noise orthose that generate electromagnetic radiation that may cause malfunctionof other electronic components are covered by the electromagnetic noisesuppressor of the present invention, thereby to control electromagneticnoise that is generated by the electronic components or that may affectother electronic components. Such electoronic apparatuses include anyelectronic components that transmit and/or receive signals. The articlewith an electromagnetic noise suppressing function of the presentinvention is an article of which the surface is at least partly coveredby the electromagnetic noise suppressor of the present invention.

(Printed Wiring Board)

The article with an electromagnetic noise suppressing function of thepresent invention is at least one printed wiring board, of anelectoronic apparatus having printed wiring board, of which at least onesurface is covered by the electromagnetic noise suppressor of thepresent invention over part or entire surface thereof. That is, theprinted wiring board may be covered over the entire surface either onboth sides or on one side thereof, or partly on both sides or on oneside thereof. The printed wiring board may be entirely covered by theelectromagnetic noise suppressor so as to absorb incomingelectromagnetic radiation as long as electromagnetic radiation generatedby the electronic components mounted on the printed wiring board do notadversely affect the other electronic components mounted on the sameprinted wiring board.

In the case in which electromagnetic radiation generated by theelectronic components mounted on the printed wiring board has anadversel effect on the other electronic components mounted on the sameprinted wiring board, electronic components other than those whichgenerate the harmful electromagnetic radiation may be enclosed by ashield box or the electromagnetic noise suppressor, while covering theelectronic components that generate the harmful electromagneticradiation individually with the electromagnetic noise suppressor.

Since the electromagnetic noise suppressor of the present invention hasflexibility, it is capable of securely covering the electroniccomponents while adapting to the deformation of the printed wiring boardeven when the printed wiring board deforms due to stress, in the case inwhich the printed wiring board is flexible.

FIG. 17 and FIG. 18 show a camera module as an example of the articlewith an electromagnetic noise suppressing function. The camera modulecomprises a printed wiring board 42 that has an image sensor 41 mountedon the surface thereof, a lens 43 that corresponds to the image sensor41, a camera holder 44 that holds the lens 43 and encloses the imagesensor 41 on the printed wiring board 42, an outer case 45 that fits onthe outside of the camera holder 44, and the electromagnetic noisesuppressor 1 that covers the surface of the outer case 45.

Covering of the outer case 45 with the electromagnetic noise suppressor1 is carried out, for example, as follows. The outer case 45 that is astructure formed from a resin by injection molding is dipped in epoxyresin solution that is a binding agent so as to cover the surface withepoxy resin of B stage having a thickness of 15 μm. Then a compositelayer is formed on the epoxy resin by physical vapor deposition toequivalent thickness of 45 nm. The outer case 45 having theelectromagnetic noise suppressing function is fitted onto the cameraholder 44, thereby shielding the camera module from noise.

FIG. 19 shows a printed wiring board as another example of the articlewith an electromagnetic noise suppressing function. The printed wiringboard comprises a circuit 52 formed on a substrate 51, a semiconductorpackage 53 and a chip component 54 that are connected to the circuit 52,and the electromagnetic noise suppressor 1 that covers the surface ofthe printed wiring board together with the circuit 52, the semiconductorpackage 53 and the chip component 54.

Covering of the printed wiring board with the electromagnetic noisesuppressor 1 is carried out, for example, as follows. An insulatingbinding agent is applied to the printed wiring board to a thickness ofabout 50 μm so as to cover the circuit 52, the semiconductor package 53and the chip component 54. The magnetic material is applied onto thebinding agent by physical vapor deposition so as to form the compositelayer. This process is not a wet process and does not require washingoperation to remove ions, and is capable of easily producing theelectromagnetic noise suppressing function.

(Electric Connector)

In the case in which the article with an electromagnetic noisesuppressing function of the present invention has at least a printedwiring board and an electric connector that transmits signals to thecircuit and the electromagnetic noise suppressor of the presentinvention is provided on at least a part of the electric connector, thenelectromagnetic radiation is prevented from entering from the outsideinto the electric connector and generating signals which causemalfunctions. In this case, too, since the electromagnetic noisesuppressor of the present invention has flexibility, it is capable ofsecurely covering the flexible connector while adapting to thedeformation of the connector even when the connector deforms due toexternal stress, in the case in which the electric connector isflexible. Examples of the article as described above include mobiletelephone and mobile telephone with camera.

(Key Top Member for Pushbutton Switch)

The article with an electromagnetic noise suppressing function of thepresent invention may be a key top member for pushbutton switch coveredwith the electromagnetic noise suppressor of the present invention. Aspecific example of the key top member for pushbutton switch is a keytop member for pushbutton switch having the electromagnetic noisesuppressor of the present invention stacked below a decorative sheetthat is provided with a pressing portion.

The decorative sheet may be made of a thermoplastic resin such aspolyester, polyurethane, polycarbonate, acryl, vinyl chloride,polyethylene or polypropylene. When the ease of printing and forming istaken into consideration, polyester, polycarbonate, acryl or alloy orcopolymer thereof is preferably used.

The decorative sheet may bear letters, symbols, pictures or the likeprinted at predetermined positions thereon as required. There is norestriction on the printing method, and a conventional printing methodmay be employed. Decoration may also be made by plating, vapordeposition, hot stamping, laser marking or other method.

The pressing portion may be formed by providing recess in the decorativesheet by drawing process or the like, and filling the recess with aresin, elastomer or the like, or by bonding a molding of pushbuttonshape made of resin or elastomer on one side of a flat decorative sheet.There is no restriction on the resin or elastomer that fill the recessof the decorative sheet or that are provided on the decorative sheet.

The electromagnetic noise suppressor is stacked on the lower surface ofthe decorative sheet that is provided with the pressing portion. In thecase of the decorative sheet having the recess filled with resin,elastomer or the like, the electromagnetic noise suppressor is appliedso as to cover both the bottom of the resin, elastomer or the like thatfills the recess and the surface of the decorative sheet where therecess is provided. In the case of the decorative sheet provided withthe molding of pushbutton shape, the electromagnetic noise suppressor isapplied to the surface opposite to that where the decorative sheet isprovided.

The article with an electromagnetic noise suppressing function of thepresent invention is exemplified by a key top member for pushbuttonswitch comprising a click sheet having click members arranged thereonand key tops provided on the click sheet, where the electromagneticnoise suppressor of the present invention is provided on one side of theclick sheet.

The key top member for pushbutton switch may have such a constitution asthe click member has an inverted dome shape and a movable contact madefrom an electrically conductive film is provided at least on the innersurface of the dome-shaped click member (bottom surface of the clicksheet), so that depressing the key top causes the click member to deformand make contact with a fixed contact provided on the printed wiringboard that is provided below.

The electromagnetic noise suppressor may be provided either on the keytop side surface of the click sheet, or on the surface opposite to thekey top. In the case in which the electromagnetic noise suppressor isprovided on the surface opposite to the key top, the electromagneticnoise suppressor is provide so as to be electrically insulated from themovable contact. That is, the electromagnetic noise suppressor may beprovided on the surface of the click sheet except for the portion wherethe movable contact is provided, or the electromagnetic noise suppressormay be provided over the entire surface of the click sheet with themovable contact being provided via an insulating film in at least upperportion on the inner surface of the dome-shaped click member.

When the electromagnetic noise suppressor is electrically insulated fromthe movable contact, interference with other keys can be suppressedduring key scan. When the electromagnetic noise suppressor is providedover the entire surface on one side of the dome-shaped click member,electromagnetic radiation in millimeter wavelength band can be preventedfrom leaking.

The click sheet is preferably made of a polyester resin such aspolyethylene terephthalate, polyethylene naphthalate, in view of theproperty to deform when pressed, property to restore by resilience whenthe pressure is removed, moldability and other factors. While there isno restriction on the material that makes the movable contact, silver,copper, carbon or the like is preferably used.

(Insert Sheet for Preform)

The article with an electromagnetic noise suppressing function of thepresent invention may be an insert sheet for a preform that has theelectromagnetic noise suppressor of the present invention provided on atleast one side thereof.

The insert sheet for a preform is formed on the surface of a moldedarticle used in the front panel of an AV apparatus, instrument panel ofan automobile, pushbutton or the like, and comprises a translucent basematerial and a translucent printing layer. The translucent printinglayer may be provided over one surface of the translucent base material,or the translucent printing layer may be sandwiched by two translucentbase layers. The insert sheet for preform of the present invention isparticularly useful when formed on the surface of a molded article usedin a pushbutton switch.

In the case of an insert sheet that has the translucent printing layerprovided over one surface of the translucent base material, theelectromagnetic noise suppressor is preferably provided on a surfacedifferent from the translucent printing layer, while it may be providedon either surface of the translucent base material in the case in whichthe translucent printing layer is sandwiched by two translucent baselayers.

An electrically conductive layer is preferably provided on the surfaceopposite to the translucent base material of the electromagnetic noisesuppressor. The electrically conductive layer may be, for example, ametal foil, vapor-deposited metal film or printed electricallyconductive paste. Providing the electrically conductive layer enables itto reflect electromagnetic radiation, prevent it from escaping to theoutside and absorb the reflection. Antenna effect can be suppressed andmetallic gloss can be provided by decreasing the Q value of resonance.

(Semiconductor Integrated Circuit)

To give electromagnetic noise suppressing function to a semiconductorintegrated circuit, the magnetic material is applied to a thickness ofabout 10 to 50 nm by physical vapor deposition to form a composite layeron an organic insulating film of thickness from 200 nm to 100 μm that isformed from polyimide, polyparaxylene, polytetrafluoroethylene, polyarylether, polyxylene, polyadamantane ether, polybenzoxazole orbenzocyclobutene resin. The composite layer may also be formed partiallyby using a mask as required. Since this is a dry process, there is noinfluence of ionic impurity and there is no need of cleaning, and theprocess is preferable for the application to semiconductor wafers. Whenthe electromagnetic noise suppressor having heterogeneous structure ofnanometer scale is provided in the vicinity of microscopic semiconductorcircuit, it is made possible to suppress the resonance of a digitalcircuit during pulse transmission and suppress radiation noise frombeing generated by impedance mismatch, thereby to improve thetransmission characteristic such as transmission speed, even with asmall amount of magnetic material.

(Action)

The electromagnetic noise suppressor of the present invention describedabove has a high resonance frequency supposedly because the compositelayer is formed where the magnetic material and the binding agent areintegrated so that even a small amount of the magnetic material canachieve the quantum effect originating from the heterogeneous structureof nanometer scale, magnetic anisotropy of the material, morphologicalmagnetic anisotropy or anisotropy due to external magnetic field,although theoretical explanation has not been presented. It isconsidered that such a feature enables it to achieve high magneticcharacteristics and electromagnetic noise suppressing effect in a highfrequency band with just a small amount of the magnetic material.

Since the electromagnetic noise suppressor of the present invention canachieve the electromagnetic noise suppressing effect even with a smallamount of the magnetic material, the amount of the magnetic material canbe reduced significantly, resulting in weight reduction.

Also since the electromagnetic noise suppressor of the present inventioncan achieve sufficient electromagnetic noise suppressing effect evenwith the composite layer of small thickness, the electromagnetic noisesuppressor can be formed with small thickness, so as to decrease thespace requirement.

In the case in which the composite layer is formed by physical vapordeposition of the magnetic material onto the base material, the magneticmaterial is dispersed in the binding agent so that the magnetic materialand the binding agent are integrated to provide high electromagneticnoise suppressing effect. The composite layer does not contain impurityions so that there is no possibility of damage on the electronic circuitby the impurity ions.

Since the amount of the magnetic material can be reduced significantly,decrease in flexibility and in strength of the resin or rubber due tothe magnetic material can me minimized in the case in which the bindingagent is resin or rubber.

Moreover, if the binding agent is a hardening resin, the magneticmaterial is distributed uniformly in the binding agent prior to curingand, after curing, the magnetic material can be suppressed fromcrystallizing into fine particles even when the electromagnetic noisesuppressor is used at a high temperature, thus improving theweatherability.

The article with an electromagnetic noise suppressing function of thepresent invention (for example, printed wiring board or semiconductorintegrated circuit) enables it to dispose the noise suppressor in thevicinity of the noise source and efficiently suppress electromagneticnoise in high-frequency band.

EXAMPLES

(Evaluation)

Electromagnetic noise suppressing characteristic (transmissionattenuation and reflection attenuation) in the vicinity of theelectromagnetic noise suppressor was measured in Examples 1 to 4 andComparative Example 1 at measuring frequency of 2 GHz by disposing atest sheet 65 of the electromagnetic noise suppressor via an insulationfilm 64 on a test fixture 62, using the test fixture 62 (TF-3Amanufactured by KEYCOM Corporation) whereon a micro-strip line 61 of 50Ω is formed and a network analyzer 63 (vector network analyzer 37247Cmanufactured by Anritsu Company Ltd.) that is connected to themicro-strip line 61 as shown in FIG. 20.

Example 1

A composite layer was formed by sputtering Mn—Zn-based high magneticpermeability ferrite to equivalent thickness of 3 nm by opposing targettype magnetron sputtering process on a polyethylene phthalate(hereinafter referred to as PET) film used as the base material having athickness of 12 μm, elastic modulus in shear of 3.8×10⁹ (Pa), carbondioxide gas permeability of 1×10⁻¹¹ [cm³ (STP) cm/(cm²×s×cmHg)] and meansurface roughness of 1.8 μm. Surface resistivity of the composite layerwas measured by DC 4-terminal method. The film was trimmed to apredetermined size, and ten sheets of this film were stacked one onanother via polyester adhesive. The stack was consolidated by vacuumpress thereby making the electromagnetic noise suppressor measuring 138μm in total thickness. Then specific gravity and electromagnetic noisesuppressing characteristic were measured. The results are shown in Table1.

Example 2

A silicone rubber having a thickness of 20 μm, elastic modulus in shearof 1×10⁷ (Pa), carbon dioxide gas permeability of 2.2×10⁻⁷ [cm³ (STP)cm/(cm²×s×cmHg)] was provided as the base material on a PET film used asthe support layer having a thickness of 25 μm, and thereon compositelayer was formed by sputtering Fe—Ni-based soft magnetic metal toequivalent thickness of 20 nm by the opposing target type magnetronsputtering process. Surface resistivity of the composite layer wasmeasured by DC 4-terminal method. The film was trimmed to apredetermined size, and thereby making the electromagnetic noisesuppressor measuring 45 μm in total thickness. Then specific gravity andelectromagnetic noise suppressing characteristic were measured. Theresults are shown in Table 1.

Example 3

A urethane gel having a thickness of 10 μm, elastic modulus in shear of1.7×10⁶ (Pa), carbon dioxide gas permeability of 5.3×10⁻⁸ [cm³ (STP)cm/(cm²×s×cmHg)] was provided as the base material on a PET film used asthe support layer having a thickness of 25 μm, and thereon a compositelayer was formed by sputtering Fe—Si—Al-based soft magnetic metal toequivalent thickness of 15 nm by magnetron sputtering process(non-opposing target type). Surface resistivity of the composite layerwas measured by DC 4-terminal method. Urethane gel was applied to thecomposite layer to a thickness of 2 μm, and sputtering was carried outagain. This process was repeated to form three composite layers therebyto obtain the electromagnetic noise suppressor measuring 79 μm in totalthickness. Then specific gravity and electromagnetic noise suppressingcharacteristic were measured. The results are shown in Table 1.

Example 4

Three composite layers were formed by sputtering Fe—Si—Al-based softmagnetic metal to equivalent thickness of 15 nm similarly to Example 3,except for employing the opposing target type magnetron sputteringprocess, thereby to obtain the electromagnetic noise suppressormeasuring 79 μm in total thickness. Characteristics were evaluatedsimilarly to Example 3. The results are shown in Table 1.

Comparative Example 1

A paste made by adding 5 parts by weight of a polyurethane resin, 1 partby weight of an isocyanate compound as a curing agent and 30 parts byweight of a solvent (1:1 mixture of cyclohexanon and toluene) to 94parts by weight of Fe—Ni-based soft magnetic metal powder of flake shape(mean particle size 15 μm, aspect ratio 65) was applied by bar coatingmethod to a support fixture for application to form a film having athickness of 1.1 mm after drying. The film was fully dried, pressedunder heat in vacuum and cured at 85° C. for 24 hours, before beingremoved from the support fixture for application, thereby to obtain theelectromagnetic noise suppressor having a thickness of 1 mm. Thenspecific gravity and electromagnetic noise suppressing characteristicwere measured. The results are shown in Table 1. TABLE 1 ComparativeExample 1 Example 2 Example 3 Example 4 Example 1 Support layer None PETPET PET None Thickness of support layer (μm) — 25 25 25 — Base materialPET Silicone Urethane gel Urethane gel None rubber Elastic modulus inshear (Pa) 3.8 × 10⁹ 1 × 10⁷ 1.7 × 10⁶ 1.7 × 10⁶ — Carbon dioxide gaspermeability     1 × 10⁻¹¹ 2.2 × 10⁻⁷   5.3 × 10⁻⁸  5.3 × 10⁻⁸ — [cm³(STP) cm/(cm² × s × cmHg)] Thickness of base material (μm) 12 20 10 10 —Magnetic material Mn—Zn-based Fe—Ni Fe—Si—Al Fe—Si—Al Fe—Ni ferriteDeposited amount (equivalent 3 20 15 15 — thickness, nm) Physical vapordeposition method Opposing Opposing Magnetron Opposing — target typetarget type target type Surface resistivity (Ω/□)   3 × 10⁷ 2 × 10²   1× 10³   4 × 10⁵ 1 × 10⁶ Number of layers stacked 10 1 3 3 — Thickness ofadhesive (μm) 2 — 2 2 — Total thickness of 138 45 79 79 1000electromagnetic noise suppressor (μm) The amount of magnetic material 3020 45 45 — deposited (equivalent thickness, nm) Specific gravity 1.3 1.21.2 1.2 6.1 Transmission attenuation (dB, −7 −8 −15 −18 −6 measured atfrequency 2 GHz) Reflection attenuation (dB, −20 −10 −12 −14 −8 measuredat frequency 2 GHz) Rupture strength (MPa) 205 10.5 21 21 2.5 Ruptureelongation (MPa) 149 450 687 687 7 Appearance Comparable Thin, lightThin, light Thin, light Heavy and strength to in weight and in weightand in weight and brittle base material expandable flexible flexibleEvaluation Good Good Good Good Poor

In Table 1, specific gravity is that of the composite layer and thesupport material combined (measured together with PET when PET is usedas the base material). Rupture strength and rupture elongation weremeasured without the support layer.

Table 1 shows that the electromagnetic noise suppressors of Examples 1to 4 and Comparative Example 1 have substantially similarelectromagnetic noise suppressing characteristic. However, theelectromagnetic noise suppressor of Comparative Example 1 has highspecific gravity of 6.1 and is brittle, and is prone to breakage whensubjected to impact. The electromagnetic noise suppressor of Example 1,in contrast, has strength and flexibility that are comparable to thoseof polyethyleneterephthalate used as the base material. Theelectromagnetic noise suppressor of Example 2 has small total thicknessof 45 μm, light in weight, expandable and flexible, thus showingrobustness and ease of processing. The electromagnetic noise suppressorof Example 3 is also thin, light in weight and flexible. Comparisonbetween Example 3 and Example 4 shows that the opposing target typemagnetron sputtering process is superior to the conventional magnetronsputtering process (non-opposing target) in achieving unevendistribution of ultra-fine particles of magnetic material.

(Evaluation)

Examples 5 to 7 and Comparative Examples 2 to 4 were evaluated asfollows.

Observation of surface: Surface was observed with magnification factorof 4000 by a laser microscope VK-9500 manufactured by KEYENCECORPORATION.

Surface resistivity was measured by DC 4-terminal method at voltage of10V using MCP-T600 manufactured by Dia Instruments Co., Ltd.Measurements at 5 points were averaged.

The thickness of the composite layer was determined from electronmicroscope photograph (50000×) of a cross section of the electromagneticnoise suppressor using a scanning electron microscope (SEM) JEM-2100Fmanufactured by JEOL Ltd.

Electromagnetic noise suppressing characteristic: S11 (reflectioncharacteristic) and S21 (transmission characteristic) were measured by Sparameter method using a near field electromagnetic noise suppressormeasuring instrument manufactured by KEYCOM Corporation. Vector networkanalyzer 37247C manufactured by Anritsu Company Ltd. and test fixturesTF-3A and TF-18A manufactured by KEYCOM Corporation were used.

Example 5

Silicone rubber having a thickness of 20 μm, elastic modulus in shear of3.8×10⁹ Pa at normal temperature, carbon dioxide gas permeability of2.2×10⁻⁷ [cm³ (STP) cm/(cm²×s×cmHg)] at normal temperature (containingwet silica) was provided as the base material on a PET film used as thesupport layer having a thickness of 12 μm, and thereon composite layerwas formed by sputtering Fe—Ni-based soft magnetic metal to equivalentthickness of 30 nm by physical vapor deposition of opposing target typemagnetron sputtering process. Sputtering was carried out by applying alow negative voltage so as to impart energy of 8 eV to the vaporizedparticles while maintaining the base material at the normal temperature.Surface resistivity of the composite layer was measured by DC 4-terminalmethod. The film was trimmed to a predetermined size, and thereby makingthe electromagnetic noise suppressor measuring 32 μm in total thickness.Surface was observed before and after sputtering. Then a thin portionwas sliced by means of a microtome from the electromagnetic noisesuppressor thus obtained and, after polishing the cut surface by ionbeam, thickness of the composite layer was measured. The measurement ofelectromagnetic noise suppressing characteristic was also conducted.

The results are shown in Table 2. Results of surface observation areshown in FIGS. 4 to 7, observation of the composite layer on the crosssection is shown in FIG. 3, and electromagnetic noise suppressingcharacteristic at frequencies from 0.05 to 3 GHz are shown in FIG. 21.In FIG. 21, thick line shows transmission attenuation when incomingelectromagnetic radiation is set to reference value (0), and thin lineshows reflection attenuation.

Example 6

A silicone gel having a thickness of 60 μm, elastic modulus in shear of5×10⁴ Pa at normal temperature, carbon dioxide gas permeability of2×10⁻⁷ [cm³ (STP) cm/(cm²×s×cmHg)] at normal temperature was provided asthe base material on a support layer similar to that of Example 5, andthereon a composite layer was formed by physical vapor deposition ofFe—Ni-based soft magnetic metal to equivalent thickness of 80 nm bybiased magnetron sputtering method thereby to obtain an electromagneticnoise suppressor having total thickness of 72 μm. Sputtering was carriedout by controlling the bias voltage so as to impart energy of 20 eV tothe vaporized particles while maintaining the base material at thenormal temperature. Surface resistivity, thickness of the compositelayer and electromagnetic noise suppressing characteristic were measuredsimilarly to Example 5.

The results are shown in Table 2. Electromagnetic noise suppressingcharacteristic at frequencies from 0.05 to 18 GHz is shown in FIG. 22.In FIG. 22, the thick line shows transmission attenuation when incomingelectromagnetic radiation is set to reference value (0), and thin lineshows reflection attenuation.

Example 7

A polyacrylonitrile sheet (hereinafter referred to as PAN) having athickness of 100 μm, elastic modulus in shear of 1.7×10⁹ Pa at thenormal temperature, elastic modulus in shear of 1.5×10⁶ Pa at 160° C.,carbon dioxide gas permeability of 5.3×10⁻⁸ [cm³ (STP) cm/(cm²×s×cmHg)]at the normal temperature and oxygen gas permeability of 2.8×10⁻¹⁵ [cm³(STP) cm/(cm²×s×cmHg)] at the normal temperature was provided as thebase material, and thereon a composite layer was formed by physicalvapor deposition of metal Ni to an equivalent thickness of 60 nm byopposing target type magnetron sputtering process thereby to obtain theelectromagnetic noise suppressor having total thickness of 100 μm.Sputtering was carried out by controlling the bias voltage so as toimpart energy of 100 eV to the vaporized particles while maintaining thebase material temperature at 160° C. Surface resistivity, thickness ofthe composite layer and electromagnetic noise suppressing characteristicwere measured similarly to Example 6.

The results are shown in Table 2. Electromagnetic noise suppressingcharacteristic at frequencies from 0.05 to 18 GHz is shown in FIG. 23.In FIG. 23, the thick line shows transmission attenuation when incomingelectromagnetic radiation is set to reference value (0), and thin lineshows reflection attenuation.

Comparative Example 2

A paste made by adding 5 parts by weight of a polyurethane resin, 1 partby weight of an isocyanate compound as a curing agent and 30 parts byweight of a solvent (1:1 mixture of cyclohexanone and toluene) to 94parts by weight of Fe—Ni-based soft magnetic metal powder, of flakeshape (mean particle size 15 μm, aspect ratio 65) having non-conductivefilm formed by oxidization of the surface, was applied by bar coatingmethod to a support fixture for application to form a film having athickness of 1.1 mm after drying. The film was fully dried, pressedunder heat in vacuum and cured at 85° C. for 24 hours, before beingremoved from the support fixture for application, thereby to obtain theelectromagnetic noise suppressor having a thickness of 1 mm. Thensurface resistivity and electromagnetic noise suppressing characteristicwere measured similarly to Example 6.

The results are shown in Table 2. Electromagnetic noise suppressingcharacteristics at frequencies from 0.05 to 3 GHz is shown in FIG. 24.In FIG. 24, the thick line shows transmission attenuation when incomingelectromagnetic radiation is set to reference value (0), and thin lineshows reflection attenuation.

Comparative Example 3

Operations similar to those of Comparative Example 2 were carried outexcept for using an Fe—Ni-based soft magnetic metal powder having meanparticle size of 8 μm and aspect ratio of 31 and forming a film 0.03 mmin thickness. Surface resistivity and electromagnetic noise suppressingcharacteristic were measured similarly to Example 6.

The results are shown in Table 2. Electromagnetic noise suppressingcharacteristic at frequencies from 0.05 to 18 GHz are shown in FIG. 25.In FIG. 25, the thick line shows the transmission attenuation whenincoming electromagnetic radiation is set to reference value (0), andthin line shows the reflection attenuation.

Comparative Example 4

Operations similar to those of Example 6 were carried out except forusing an EB vapor deposition apparatus. Particle energy was 1 eV. Auniform film of magnetic material having a thickness of 80 nm (0.08 μm)was formed without forming a composite layer.

The results are shown in Table 2. Electromagnetic noise suppressingcharacteristic at frequencies from 0.05 to 3 GHz is shown in FIG. 26. InFIG. 26, the thick line shows the transmission attenuation when incomingelectromagnetic radiation is set to reference value (0), and the thinline shows the reflection attenuation. TABLE 2 Comparative ComparativeComparative Example 5 Example 6 Example 7 Example 2 Example 3 Example 4Support layer PET PET None None None PET Thickness of support layer (μm)12 12 — — — 12 Base material Silicone Silicone PAN — — Silicone Elasticmodulus in shear during 1 × 10⁷ 5 × 10⁴ 1.5 × 10⁶ — — 5 × 10⁴  vapordeposition (Pa) Thickness of base material (μm) 20 60 100 — — 60Magnetic material Fe—Ni Fe—Ni Ni Fe—Ni Fe—Ni Fe—Ni Deposited amount(equivalent 30 80 60 — — 80 thickness, nm) Particle energy (eV) 8 20 100— — — Thickness of composite layer (or 0.04 15.0 1.1 1000 30 0.08 layercontaining magnetic material) (μm) Maximum transmission attenuation of−11.9 −30.2 −32.9 −37.0 −0.8 −12.8 electromagnetic radiation (dB)Frequency for maximum transmission 3.0 18.0 15.7 2.8 10.5 1.5attenuation of electromagnetic radiation (GHz) Reflection attenuation atthe above −8.4 −10.7 −9.1 −9.1 −18.5 −1.0 frequency (dB) Surfaceresistivity (Ω/□) 2 × 10² 5 × 10⁵   1 × 10³ 1 × 10⁶ 1 × 10⁶ 3 × 10⁻²Maximum transmission attenuation of 298 2.01 29.9 0.037 0.027 160electromagnetic radiation per unit thickness of composite layer (orlayer containing magnetic material) (dB/μm) Evaluation Good Good GoodPoor Poor Poor

From Table 2 and FIGS. 21 to 25, it can be seen that Examples 5 to 7 andComparative Examples 2 and 3 have similar electromagnetic noisesuppressing characteristics, that is they show similar curves oftransmission attenuation and reflection attenuation, with large value ofreflection attenuation and small value of transmission attenuation inlow frequency region, and transmission attenuation increasing with thefrequency.

In Examples 5 to 7, the amount of the magnetic material and maximumtransmission attenuation of electromagnetic radiation show a correlationwith each other, such that a larger amount of the magnetic materialresults in larger attenuation. The composite layer is thin and showstransmission attenuation and reflection attenuation characteristicscomparable to those of Comparative Example 4.

In Comparative Example 2, the layer containing the magnetic material(the same as the electromagnetic noise suppressor in total thickness) isas thick as 1000 μm and shows transmission attenuation and reflectionattenuation comparable to those of Example, although the layer includesless content of the binding agent and is therefore prone to breakagewhen subjected to impact. The transmission attenuation is alsoinsufficient at low frequencies, and the band is narrower than that ofthe Examples.

In Comparative Example 3, although the layer is thin, absorbingcharacteristics becomes poorer accordingly, resulting in smaller valueof maximum transmission attenuation of electromagnetic radiation perunit thickness of the layer including the magnetic layer similarly toComparative Example 2. Maximum transmission attenuation ofelectromagnetic radiation does not reach −10 dB, which shows thatpractical electromagnetic noise suppressing effect cannot be obtained.

In Comparative Example 4, since vapor deposition was carried out withlow particle energy, a uniform thin metal film was formed on the surfaceof the base material showing a behavior similar to metal as shown inFIG. 26 and a peak characteristics to metal, thus achieving transmissionattenuation due to reflection. The electromagnetic noise suppressingeffect is low and the function as an electromagnetic shield ispreformed.

The electromagnetic noise suppressors of Examples 5 to 7 have largemaximum transmission attenuation of electromagnetic radiation/thicknessof composite layer, showing excellent electromagnetic noise suppressingcharacteristic per thickness, and is thin, light in weight, expandableand flexible while retaining the properties of the binding agent.

(Evaluation)

Examples 8 to 10 and Comparative Examples 5 to 7 were evaluated asfollows.

Observation of surface: Surface was observed with magnification factorof 4000 by a laser microscope VK-9500 manufactured by KEYENCECORPORATION.

Surface resistivity was measured by DC 4-terminal method at voltage of10V using MCP-T600 manufactured by Dia Instruments Co., Ltd.Measurements at 5 points were averaged.

The thickness of the composite layer was determined from electronmicroscope photograph (50000×) of a cross section of the electromagneticnoise suppressor using a scanning electron microscope (SEM) JEM-2100Fmanufactured by JEOL Ltd.

Electromagnetic noise suppressing characteristic: S21 (transmissionattenuation) and S11 (reflection attenuation) were measured by Sparameter method using a near field electromagnetic noise suppressormeasuring instrument manufactured by KEYCOM Corporation. Vector networkanalyzer 37247C manufactured by Anritsu Company Ltd. and test fixturesTF-3A manufactured by KEYCOM Corporation was used for micro-strip lineof 50 Ω. Power loss at 1 GHz was determined from S21 and S11 at 1 GHz.

Example 8

Silicone rubber having a thickness of 20 μm, elastic modulus in shear of1×10⁷ Pa at normal temperature, carbon dioxide gas permeability of2.2×10⁻⁷ [cm³ (STP) cm/(cm²×s×cmHg)] at normal temperature (containingwet silica) was provided as the base material on a PET film used as thesupport layer having a thickness of 12 μm, and thereon composite layerwas formed by sputtering Fe—Ni-based soft magnetic metal to equivalentthickness of 30 nm by physical vapor deposition of opposing target typemagnetron sputtering process. Sputtering was carried out by applying alow negative voltage so as to impart energy of 8 eV to the vaporizedparticles while maintaining the base material at the normal temperature.Surface resistivity of the composite layer was measured by a DC4-terminal method. The film was trimmed to a predetermined size, andthereby making the electromagnetic noise suppressor measuring 32 μm intotal thickness. Then, a thin portion was sliced by means of a microtomefrom the electromagnetic noise suppressor thus obtained and, afterpolishing the cut surface by ion beam, thickness of the electromagneticnoise suppressing layer was measured. The measurement of electromagneticnoise suppressing characteristic was also conducted.

The results are shown in Table 3. Power loss characteristics atfrequencies from 0.05 to 3 GHz are shown in FIG. 27.

Example 9

Acrylic adhesive layer (hereinafter referred to as AC, product name1604N manufactured by Soken Chemical & Engineering Co., Ltd.) having athickness of 25 μm, elastic modulus in shear of 6×10⁴ Pa at normaltemperature, carbon dioxide gas permeability of 2×10⁻⁸ [cm³ (STP)cm/(cm²×s×cmHg)] at normal temperature was provided as the base materialon a polyimide film (hereinafter referred to as PI) used as the supportlayer having a thickness of 6 μm, and thereon Fe—Ni-based soft magneticmetal was deposited to equivalent thickness of 30 nm by physical vapordeposition of biased magnetron sputtering process, thereby to obtain theelectromagnetic noise suppressor having total thickness of 72 μm.Sputtering was carried out by controlling the bias voltage so as toimpart energy of 10 eV to the vaporized particles while maintaining thebase material at the normal temperature. Surface resistivity, thicknessof the composite layer and electromagnetic noise suppressingcharacteristic were measured similarly to Example 8.

The results are shown in Table 3. Power loss characteristics atfrequencies from 0.05 to 3 GHz are shown in FIG. 28.

Example 10

A PAN sheet having a thickness of 70 μm, elastic modulus in shear of1.7×10⁹ Pa at the normal temperature, elastic modulus in shear of1.5×10⁶ Pa at 160° C., carbon dioxide gas permeability of 5.3×10⁻⁸ [cm³(STP) cm/(cm²×s×cmHg)] at normal temperature and oxygen gas permeabilityof 2.8×10⁻¹⁵ [cm³ (STP) cm/(cm²×s×cmHg)] at normal the temperature wasprovided as the base material, and thereon metal Ni was deposited toequivalent thickness of 50 nm by physical vapor deposition of opposingtarget type magnetron sputtering process thereby to obtain theelectromagnetic noise suppressor having total thickness of 100 μm.Sputtering was carried out by controlling the bias voltage so as toimpart energy of 20 eV to the vaporized particles while maintaining thebase material temperature at 160° C. Surface resistivity, thickness ofthe composite layer and electromagnetic noise suppressing characteristicwere measured similarly to Example 9.

The results are shown in Table 3. Power loss characteristic atfrequencies from 0.05 to 3 GHz is shown in FIG. 29.

Comparative Example 5

A paste made by adding 5 parts by weight of a polyurethane resin, 1 partby weight of an isocyanate compound as a curing agent and 30 parts byweight of a solvent (1:1 mixture of cyclohexanone and toluene) to 94parts by weight of Fe—Ni-based soft magnetic metal powder, of flakeshape (mean particle size 15 μm, aspect ratio 65) having non-conductivefilm formed by oxidization of the surface, was applied by bar coatingmethod to a support fixture for application to form a film having athickness of 0.51 mm after drying. The film was fully dried, pressedunder heat in a vacuum and was cured at 85° C. for 24 hours, beforebeing removed from the support fixture for application, thereby toobtain the electromagnetic noise suppressor having a thickness of 0.5mm. Then surface resistivity and electromagnetic noise suppressingcharacteristic were measured similarly to Example 9.

The results are shown in Table 3. Power loss characteristic atfrequencies from 0.05 to 3 GHz is shown in FIG. 30.

Comparative Example 6

An amorphous film 2.5 μm in thickness was formed on a glass plate 0.6 mmthick using a high frequency magnetron sputtering apparatus and aCo—Fe—Al target in a stream of oxygen gas. Then a magnetic field of19894 A/m (250 Oe) was applied so as to heat the sample to 300° C.,thereby causing metallic crystals to precipitate.

It was confirmed, through observation under a transmission electronmicroscope, that the metallic crystal had nano-granular structureconsisting of granules measuring several nanometers and insulatingoxide. Surface resistivity and thickness of the amorphous film weremeasured similarly to Example 9. The film was divided by means of adicing saw (blade thickness 0.15 mm) at 2.5 mm intervals so as to beinsulated, and electromagnetic noise suppressing characteristic wasmeasured.

The results are shown in Table 3. Power loss characteristic atfrequencies from 0.05 to 3 GHz is shown in FIG. 31.

Comparative Example 7

An aqueous solution of ferrous chloride (16.6 mmol/l), nickel (II)chloride (15.3 mmol/l) and zinc chloride (0.18 mmol/l) and an oxidizingsolution consisting of sodium nitrate (5 mmol/l) and ammonium acetate(65 mmol/l) were applied, each at a flow rate of 50 ml/min., to a PIfilm having a thickness of 50 μm by spin spray coating for about 15hours until nickel-zinc-ferrite plating film 15 μm in thickness wasformed, that was then washed in water thereby to obtain a specimen.Surface resistivity, thickness of the nickel-zinc-ferrite plating filmand electromagnetic noise suppressing characteristic were measuredsimilarly to Example 9.

The results are shown in Table 3. Power loss characteristics atfrequencies from 0.05 to 3 GHz are shown in FIG. 32. TABLE 3 ExampleComparative Comparative Comparative Example 8 Example 9 10 Example 5Example 6 Example 7 Support layer PET PI None None Glass PI Thickness ofsupport layer (μm) 12 6 — — 600 50 Base material Silicone AC PAN — — —Elastic modulus in shear during 1 × 10⁷ 6 × 10⁴ 1.5 × 10⁶ — — — vapordeposition (Pa) Thickness of base material (μm) 20 25 70 — — — Magneticmaterial Fe—Ni Fe—Ni Ni Fe—Ni Co—Fe—Al—O Ni—Zn—Fe—O Deposited amount(equivalent 30 50 50 — — — thickness, nm) Particle energy (eV) 8 10 20 —— — Thickness of composite layer (or 0.04 0.06 0.15 500 2.0 15.0 layercontaining magnetic material) (μm) Transmission attenuation (dB at 1GHz) −4.0 −7.8 −12.6 −0.8 −0.9 −1.9 Reflection attenuation (dB at 1 GHz)−6.8 −6.8 −4.1 −9.6 −11.2 −11.0 Power loss (at 1 GHz) 0.39 0.62 0.560.064 0.11 0.28 Surface resistivity (Ω/□) 2 × 10² 4 × 10³   2 × 10⁴   1× 10⁶  2 × 10⁰ 7 × 10⁷ Total thickness of electromagnetic 32 31 70 500602 65 noise suppressor (μm) Power loss/thickness (μm) of 9.75 10.3 3.731.3 × 10⁻⁴ 0.055 0.019 composite layer (or layer containing magneticmaterial) Electromagnetic noise suppressing Good Good Good InsufficientInsufficient Insufficient effect Evaluation Rubber-like Surface showsTough A little Hard and Difficult to elasticity adhesiveness filmbrittle and prone to handle due to and and cannot cracking crack and/orflexibility flexibility expand delamination shows the of ferriteproperty of layer the support member Evaluation Good Good Good Poor PoorPoor

Table 3 shows that power loss at 1 GHz is 0.3 or higher in Examples 8 to10, lower than 0.3 in Comparative Examples 5 to 7, and was lower than0.1 in Comparative Example 1. This indicates that Examples of thepresent invention have high electromagnetic noise suppressing effect inthe sub-microwave band around 1 GHz where practical effect is said to behigh. It was also found that the composite layers of Examples are verythin and show far higher values of power loss per unit thickness of thecomposite layer, about four orders of magnitude higher when compared toComparative Example 5.

FIGS. 27 to 29 that depict Examples show similar values, about 0.8, ofpower loss at 3 GHz, while FIGS. 30 to 31 that depict ComparativeExamples show lower values of about 0.5.

Increase in power loss with increasing frequency is about 0.2 at 0.5 GHzand about 0.6 at 1 GHz as shown in FIG. 27 of Example, about 0.4 at 0.5GHz and about 0.6 at 1 GHz in FIG. 28 and about 0.3 at 0.5 GHz and about0.6 at 1 GHz in FIG. 29. That is, power loss increases rapidly with thefrequency up to about 1 GHz in Examples. FIG. 30 that depicts theComparative Example, in contrast, shows an increase in power loss ofabout 0.03 at 0.5 GHz and about 0.1 at 1 GHz. FIG. 31 shows an increasein power loss of about 0.04 at 0.5 GHz and about 0.1 at 1 GHz. FIG. 32shows an increase in power loss of about 0.1 at 0.5 GHz and about 0.28at 1 GHz. That is, power loss increases gradually with the frequency upto about 1 GHz in Comparative Examples.

The electromagnetic noise suppressors of Examples were thin and light inweight and had flexibility similarly to the support member, while theelectromagnetic noise suppressors of Comparative Examples were thick,heavy and brittle.

(Evaluation)

Examples 11 to 16 and Comparative Examples 8 to 10 were evaluated asfollows.

Observation of cross section was carried out with a transmissionelectron microscope H9000NAR manufactured by Hitachi, Inc.

Electromagnetic noise suppressing characteristic: S11 (reflectionattenuation) and S21 (transmission attenuation) were measured by Sparameter method using a near field electromagnetic noise suppressormeasuring instrument manufactured by KEYCOM Corporation. Vector networkanalyzer 37247C manufactured by Anritsu Company Ltd. and test fixtureTF-3A manufactured by KEYCOM Corporation was used for micro strip lineof 50 Ω. Electromagnetic noise suppressing effect (Ploss/Pin) can bedetermined from the changes in S11 and S21 of the transmissioncharacteristics by the following equation.Ploss/Pin=1−(|S11|² +|S21|²)

Combustion test was conducted according to vertical combustion test UL94VTM. Five samples, measuring 200 mm in thickness, 50 mm in width and 0.1mm in thickness were tested. Criteria of judgment are shown in Table 4.TABLE 4 (Unit: sec.) 94VTM-0 94VTM-1 94VTM-2 Flame retaining time ofeach ≦10 ≦30 ≦30 sample (t₁ or t₂) Total flame retaining time of ≦50≦250 ≦250 each set through all processes (t₁ + t₂ of 5 samples) Sum offlame retaining time and ≦30 ≦60 ≦60 smoking time after second flamingof each sample (t₂ + t₃) Whether flame or smoke remained No No No up tothe marking line of 125 mm Whether the indicator cotton as No No Yesignited by flaming material or dripping material

Example 11

PAN having elastic modulus in shear of 1.7×10⁷ Pa at normal temperaturewas dissolved in N,N-dimethylacrylamide (hereinafter denoted DMAc), toprepare a DMAc solution of PAN having concentration of 25% by weight. 20Parts by weight of an aromatic condensed phosphate ester (PX-200manufactured by DAIHACHI CHEMICAL INDUSTRY CO., LTD.) was added as aflame retarding agent to 400 parts by weight of the solution, and thesolution was applied to PET to form a film having a thickness of 0.1 mmafter drying, thereby obtaining a PAN sheet. A composite layer wasformed by sputtering Fe—Ni-based soft magnetic metal to equivalentthickness of 20 nm on the PAN surface of the PAN sheet by physical vapordeposition of opposing target type magnetron sputtering process.Sputtering was carried out by applying a low negative voltage so as toimpart energy of 8 eV to the vaporized particles while maintaining thePAN sheet at the normal temperature.

A thin portion was sliced by means of a microtome from theelectromagnetic noise suppressor thus obtained and the cut surface,after being polished by an ion beam, was observed with a high-resolutiontransmission electron microscope. The thickness of the composite layerwas 40 nm (0.040 μm).

The measurement of electromagnetic noise suppressing characteristic at 1GHz and combustion test were also conducted. The results are shown inTable 5.

Example 12

3 Parts by weight of 2-methylimidazole (manufactured by Shikoku Corp.)as a curing agent, 20 parts by weight of triphenyl phosphate(hereinafter denoted as TPP, manufactured by DAIHACHI CHEMICAL INDUSTRYCO., LTD.) as a flame retarding agent, 50 parts by weight of aluminumhydroxide (hereinafter denoted as Al(OH)₃) and 50 parts by weight ofmagnesium hydroxide (hereinafter denoted as Mg(OH)₂) were added to 100parts by weight of epoxy resin having elastic modulus in shear of8.0×10⁶ Pa before curing and elastic modulus in shear of 5×10⁹ Pa aftercuring, and the mixture was applied to PET to form a film having athickness of 0.1 mm, thereby to obtain an epoxy resin sheet (B stage). Acomposite layer was formed by sputtering Fe—Ni-based soft magnetic metalto equivalent thickness of 15 nm on the epoxy resin surface of the epoxyresin sheet by physical vapor deposition of the opposing target typemagnetron sputtering process. Sputtering was carried out by applying alow negative voltage so as to impart energy of 8 eV to the vaporizedparticles while maintaining the epoxy resin sheet at the normaltemperature. Then the sheet was heated at 40° C. for 6 hours, then at120° C. for 2 hours to harden the epoxy resin, and then the PET wasremoved, thereby to obtain the electromagnetic noise suppressor.

A thin portion was sliced by means of a microtome from theelectromagnetic noise suppressor thus obtained. The cut surface waspolished by ion beam and was observed with high-resolution transmissionelectron microscope. The thickness of the composite layer was 25 nm(0.025 μm).

The measurement of electromagnetic noise suppressing characteristic at 1GHz and combustion test were also conducted. The results are shown inTable 5.

Example 13

0.2 parts by weight of dinitrodiamine platinum (II) as flame retardingagent and 0.1 part by weight of acetylene black were added to 100 partsby weight of silicone rubber (dual component type) containing wetsilica, and the mixture was subjected to vulcanization at 150° C. for 1hour, thereby to obtain a silicon sheet having a thickness of 0.1 mm andelastic modulus in shear of 1.5×10⁷ Pa after vulcanization. A compositelayer was formed by sputtering Fe—Ni-based soft magnetic metal toequivalent thickness of 15 nm on one side of the silicone sheet byphysical vapor deposition of the opposing target type magnetronsputtering process, thereby to obtain the electromagnetic noisesuppressor. Sputtering was carried out by applying a low negativevoltage so as to impart energy of 8 eV to the vaporized particles whilemaintaining the silicone sheet at the normal temperature.

A thin portion was sliced by means of a microtome from theelectromagnetic noise suppressor thus obtained and the cut surface waspolished by ion beam and the cross section of the composite layer wasobserved with high-resolution transmission electron microscope. Thethickness of the composite layer was 30 nm (0.030 μm).

The measurement of electromagnetic noise suppressing characteristic at 1GHz and combustion test were also conducted. The results are shown inTable 5.

Comparative Example 8

100 parts by weight of a solution A containing a binding agent preparedas described below was added to 300 parts by weight of Fe—Ni-based softmagnetic metal powder, of flake shape (mean particle size 15 μm, aspectratio 65) having non-conductive film formed by oxidization of thesurface, thereby to make a paste. The paste was applied by a bar coatingmethod to a support fixture for application to form a film having athickness of 0.1 mm after drying. The film was fully dried, pressed in avacuum and cured at 85° C. for 24 hours, before being removed from thesupport fixture for application, thereby to obtain the electromagneticnoise suppressor. The electromagnetic noise suppressor was evaluatedsimilarly to Example 11. The results are shown in Table 5.

Preparation of solution A: 60 parts by weight of a polyurethane resin,20 parts by weight of an isocyanate compound as a curing agent and 20parts by weight of an aromatic condensed phosphate ester (PX-200manufactured by DAIHACHI CHEMICAL INDUSTRY CO., LTD.) as flame retardingagent were added to 400 parts by weight of a solvent (1:1 mixture ofcyclohexanone and toluene), to prepare a solution A.

Comparative Example 9

100 Parts by weight of a silicone rubber (dual component type)containing wet silica, 0.2 parts by weight of dinitrodiamine platinum(II) as flame retarding agent and 1.0 parts by weight of acetylene blackwere added to 300 parts by weight of Fe—Ni-based soft magnetic metalpowder, of flake shape (mean particle size 15 μm, aspect ratio 65)having non-conductive film formed by oxidization of the surface, andmixed with a mixing roll, thereby to make a composite magnetic material.The composite magnetic material was rolled into a sheet 0.1 mm inthickness with two rolls, and was subjected to vulcanization at 150° C.for 1 hour, thereby to obtain electromagnetic noise suppressor. Theelectromagnetic noise suppressor was evaluated similarly to Example 11.The results are shown in Table 5. TABLE 5 Comparative ComparativeExample 11 Example 12 Example 13 Example 8 Example 9 Binding agent PANEpoxy resin Silicone Urethane resin Silicone Flame retarding agentAromatic TPP, Al(OH)₃, Dinitrodiamine Aromatic Dinitrodiamine condensedMg(OH)₂ platinum (II), condensed platinum (II), phosphate acetylenephosphate acetylene ester black ester black Magnetic material amount 2015 15 — — (equivalent thickness, nm) Thickness of composite layer 0.0400.025 0.030 — — (μm) Reflection attenuation (S11) −6.0 −7.4 −8.6 −9.8−8.8 (dB at 1 GHz) Transmission attenuation (S21) −6.8 −5.0 −7.4 −0.8−1.0 (dB at 1 GHz) Ploss/Pin (at 1 GHz) 0.54 0.50 0.68 0.06 0.07Electromagnetic noise Good Good Good Insufficient Insufficientsuppressing effect Flexible or not Yes Yes Yes Easily broken Yes byexternal stress. t₁ or t₂ (seconds) 12-22  7-11 2-5 Unable to 26-41 t₁ +t₂ of 5 samples (seconds) 158 91 36 evaluate 264 t₂ + t₃ (seconds) 15-4012-26 2-7 45-64 Whether flame or smoke No No No No remained up to themarking line of 125 mm Whether the indicator cotton No No No No wasignited by flaming material or dripping material UL94 Evaluation VTM-1VTM-1 VTM-0 Poor

Table 5 shows that satisfactory values of Ploss/Pin at 1 GHz wereachieved in Examples 11 to 13, indicating sufficient electromagneticnoise suppressing effect. In Comparative Examples 8 and 9, where thesoft magnetic material powder and the binding agent were simply mixed,Ploss/Pin at 1 GHz was 0.1 or lower when the thickness was as small as0.1 mm, indicating very low electromagnetic noise suppressing effect. InComparative Example 8, it is difficult to form a thin film of about 0.1mm, and flame retarding property could not be evaluated.

With regard to flame retarding property, the electromagnetic noisesuppressors of Examples 11 to 13 demonstrated sufficient level of flameretarding property, satisfying the requirements of VTM-1 in Examples 11and 12 and VTM-0 in Example 13. In Comparative Example 9, although theflame retarding agent comparable to that of Example 13 was added,sufficient flame retarding property could not be achieved since softmagnetic material powder was used.

Example 14

3 parts by weight of 2-methylimidazole (manufactured by Shikoku Corp.)as a curing agent was added to 100 parts by weight of epoxy resin havingelastic modulus in shear of 8.0×10⁶ Pa before curing and elastic modulusin shear of 5×10⁹ Pa after curing, and the mixture was applied to apolyimide resin film having a thickness of 25 μm (KAPTON 100ENmanufactured by DU PONT□TORAY CO., LTD.), thereby to obtain a stackconsisting of an epoxy resin of B stage and a film made of flameretarding resin. The thickness of the epoxy resin layer was 15 μm. Acomposite layer was formed by sputtering Fe—Ni-based soft magnetic metalto equivalent thickness of 10 nm on the epoxy resin surface of the stackby physical vapor deposition of an opposing target type magnetronsputtering process. Sputtering was carried out by applying a lownegative voltage so as to impart energy of 8 eV to the vaporizedparticles while maintaining the epoxy resin surface at the normaltemperature. Then the sheet was heated at 40° C. for 6 hours, then at120° C. for 2 hours to harden the epoxy resin, thereby to obtain theelectromagnetic noise suppressor.

A thin portion was sliced by means of a microtome from theelectromagnetic noise suppressor thus obtained and the cut surface waspolished by an ion beam. Cross section of the composite layer wasobserved with a high-resolution transmission electron microscope. Thethickness of the composite layer was 25 nm (0.025 μm).

The measurement of electromagnetic noise suppressing characteristic at 1GHz and combustion test were also conducted. The results are shown inTable 6.

Example 15

A silicone rubber (dual component type) containing wet silica havingelastic modulus in shear of 1.5×10⁷ Pa after vulcanization was laminatedby extrusion onto a polyethersulfon resin film 25 μm in thickness(Sumilite FS-13000 manufactured by SUMITOMO BAKELITE Co., Ltd.) and wasvulcanized at 150° C. for 1 hour, thereby to obtain a stack. Thethickness of the silicone rubber layer was 20 μm. A composite layer wasformed by sputtering Fe—Ni-based soft magnetic metal to equivalentthickness of 15 nm on the silicone side of the stack by physical vapordeposition of the opposing target type magnetron sputtering process,thereby to obtain the electromagnetic noise suppressor. Sputtering wascarried out by applying a low negative voltage so as to impart energy of8 eV to the vaporized particles while maintaining the silicone sheet atthe normal temperature.

A thin portion was sliced by means of a microtome from theelectromagnetic noise suppressor thus obtained and the cut surface waspolished by an ion beam and the cross section of the composite layer wasobserved with a high-resolution transmission electron microscope. Thethickness of the composite layer was 30 nm (0.030 μm).

The measurement of electromagnetic noise suppressing characteristic at 1GHz and combustion tests were also conducted. The results are shown inTable 6.

Example 16

PAN having an elastic modulus in shear of 1.7×10⁷ Pa at the normaltemperature was dissolved in DMAc to prepare a DMAc solution of PANhaving a concentration of 25% by weight. This solution was applied tofluororesin film having a thickness of 50 μm (Aflex 50N-NT manufacturedby ASAHI GLASS CO., LTD.) by means of a bar coater to form a PAN filmhaving a thickness of 10 μm after drying, thereby to obtain a stack. Acomposite layer was formed by sputtering Fe—Ni-based soft magnetic metalto equivalent thickness of 20 nm on the PAN surface of the stack byphysical vapor deposition of opposing target type magnetron sputteringprocess, thereby to obtain the electromagnetic noise suppressor.Sputtering was carried out by applying a low negative voltage so as toimpart energy of 8 eV to the vaporized particles while maintaining thePAN sheet at the normal temperature.

A thin portion was sliced by means of a microtome from theelectromagnetic noise suppressor thus obtained and, the cut surface waspolished by an ion beam and was observed with a high-resolutiontransmission electron microscope. The thickness of the composite layerwas 30 nm (0.030 μm).

The measurement of electromagnetic noise suppressing characteristic at 1GHz and combustion test were also conducted. The results are shown inTable 6.

Comparative Example 10

100 parts by weight of a silicone rubber (dual component type)containing wet silica was added to 300 parts by weight of Fe—Ni-basedsoft magnetic metal powder, of flake shape (mean particle size 15 μm,aspect ratio 65) having non-conductive film formed by oxidization of thesurface, and mixed with a mixing roll, thereby to make a compositemagnetic material. The composite magnetic material having a thickness of20 μm was laminated by extrusion onto a polyimide resin film having athickness of 25 μm (KAPTON 100EN manufactured by DU PONT□TORAY CO.,LTD.), and was subjected to vulcanization at 150° C. for 1 hour, therebyto obtain an electromagnetic noise suppressor. The electromagnetic noisesuppressor was evaluated similarly to Example 14. The results are shownin Table 6. TABLE 6 Comparative Example 14 Example 15 Example 16 Example10 Binding agent Epoxy resin Silicone rubber PAN Silicone rubber Flameretarding agent Polyimide resin Polyethersulfon Fluororesin Polyimideresin Thickness of 25 25 50 25 flame retarding resin layer (μm) Magneticmaterial 10 15 20 — amount (equivalent thickness, nm) Thickness of 0.0250.030 0.030 — composite layer (μm) Reflection −6.0 −8.2 −7.0 −9.5attenuation (S11) (dB at 1 GHz) Transmission −7.4 −7.9 −6.1 −0.9attenuation (S21) (dB at 1 GHz) Ploss/Pin (at 1 GHz) 0.57 0.69 0.56 0.07t₁ or t₂ (seconds) 2-4  8-14 2-5 15-24 t₁ + t₂ 40 106 34 198 of 5samples t₂ + t₃ (seconds) 2-6 11-23 0-4 24-42 Whether flame or No No NoNo smoke remained up to the marking line of 125 mm Whether the No No NoNo indicator cotton was ignited by flaming material or dripping materialUL94 Evaluation VTM-0 VTM-1 VTM-0 VTM-1 Comprehensive Excellent GoodExcellent Poor evaluation

Table 6 shows that satisfactory values of Ploss/Pin at 1 GHz wereachieved in Examples 14 to 16, indicating sufficient electromagneticnoise suppressing effect. In Comparative Example 10, where the softmagnetic material powder and the binding agent were simply mixed,Ploss/Pin at 1 GHz was 0.1 or lower when the thickness was as small as100 μm, indicating very low electromagnetic noise suppressing effect.

With regards to flame retarding property, the electromagnetic noisesuppressors of Examples 14 to 16 demonstrated sufficient level of flameretarding property, satisfying the requirements of VTM-0 in Examples 14and 16 and VTM-1 in Example 15. In Comparative Example 10, although therequirement of VTM-1 was met due to the use of flame retarding agent,electromagnetic noise suppressing effect was not exhibited despite thepresence of the composite magnetic material layer having a thickness of100 μm, and the electromagnetic noise suppressor was heavy and lessflexible since a large amount of soft magnetic material powder was used.In the comprehensive evaluation, “Excellent” indicates that highelectromagnetic noise suppressing effect and flame retarding property ofVTM-0 were achieved, “Good” indicates that high electromagnetic noisesuppressing effect and flame retarding property of VTM-1 were achieved,and “Poor” indicates that electromagnetic noise suppressing effectand/or flame retarding property were poor.

In Examples 17 to 20 and Comparative Examples 11 and 12, elastic modulusin shear of the base material was measured at the normal temperature inaccordance with JIS K 6254.

Example 17

The electromagnetic noise suppressor shown in FIG. 8 was made under thefollowing conditions.

(Base Material Containing Electrically Conductive Filler and DielectricMaterial Powder Dispersed Therein)

A silicone rubber was prepared with 15% by volume of dielectric materialpowder consisting of barium titanate having a mean particle size of 1 μmand 30% by volume of electrically conductive filler consisting ofscale-shaped silver powder having mean particle size of 3.5 μm dispersedtherein. The silicone rubber was used as the base material (elasticmodulus in shear of 8.3×10⁸ Pa, carbon dioxide gas permeability of2.1×10⁻⁷ [cm³ (STP) cm/(cm²×s×cmHg)], containing wet silica).

The base material prepared as described above was applied onto a PETfilm used as the support layer having a thickness of 12 μm and elasticmodulus in shear of 3.8×10⁹ Pa at normal temperature, thereby forming abase material layer 10 μm in thickness.

(Composite Layer)

A composite layer was formed on the surface of the base material made asdescribed above by sputtering Fe—Ni-based soft magnetic metal toequivalent thickness of 30 nm, thereby to obtain the electromagneticnoise suppressor. Sputtering was carried out by the opposing target typemagnetron sputtering process while applying a low negative voltage so asto impart energy of 8 eV to the vaporized particles while maintainingthe base material at the normal temperature.

Surface resistivity of the electromagnetic noise suppressor thusobtained was measured by DC 4-terminal method with the result of 2×10²Ω/□ and total thickness of the electromagnetic noise suppressor was 19μm.

Example 18

The electromagnetic noise suppressor shown in FIG. 13 was made under thefollowing conditions.

(Electrically Conductive Layer)

Ag Metal and Ni metal were deposited to a thickness of 45 nm and 80 nm,respectively, on a PI film 9 μm in thickness used as the support film byphysical deposition of the opposing target type magnetron sputteringprocess, there by form an electrically conductive layer having surfaceresistivity of 0.2 Ω/□ as measured by DC 4-terminal method.

(Base Material)

A base material similar to that of Example 17 except that theelectrically conductive filler was not contained (elastic modulus inshear 6.5×10⁷ Pa at the normal temperature, carbon dioxide gaspermeability 2.3×10⁻⁷ [cm³ (STP) cm/(cm²×s×cmHg)], containing wetsilica) was applied onto the metal surface of the electricallyconductive layer, thereby forming a base material layer 10 μm inthickness.

(Composite Layer)

Ferromagnetic material layer consisting of Ni metal was formed on thesurface of the base material made as described above by the opposingtarget type magnetron sputtering process to equivalent thickness of 50nm, while applying a bias voltage so as to impart energy of 100 eV tothe vaporized particles, thereby to obtain the electromagnetic noisesuppressor having surface resistivity of 6×10³ Ω/□ and total thicknessof 19.125 μm.

Example 19

The electromagnetic noise suppressor was made similarly to Example 18except for using a silicone rubber (elastic modulus in shear 1.2×10⁷ Paat normal temperature, carbon dioxide gas permeability 2.2×10⁻⁷ [cm³(STP) cm/(cm²×s×cmHg)], containing wet silica), that is, the basematerial of Example 17 minus the electrically conductive filler and thedielectric material powder dispersed therein.

Example 20

(Electrically Conductive Layer)

Electrically conductive layer was made from plain-weaved SUS mesh of#165 in the form of interlaced metal wires (wire diameter 0.05 mm, meshopening 0.104 mm, void ratio 43.9%) without providing a support film.

(Base Material)

Then a base material was formed to a thickness of 10 μm from a materialsimilar to that of Example 18 on the electrically conductive layer ofinterlaced metal wires.

(Composite Layer)

The electromagnetic noise suppressor having total thickness of 110 μmwas made by sputtering on the base material similarly to Example 18.

Comparative Example 11

A paste was prepared by adding 5 parts by weight of a polyurethaneresin, 1 part by weight of an isocyanate compound as a curing agent and30 parts by weight of a solvent (1:1 mixture of cyclohexanon andtoluene) to 94 parts by weight of Fe—Ni-based soft magnetic metal powderof flake shape having nonconductive film formed by oxidization of thesurface (mean particle size 15 μm, aspect ratio 65). This paste wasapplied to plain-weaved SUS mesh of #165 in the form of interlaced metalwires (wire diameter 0.05 mm, mesh opening 0.104 mm, void ratio 43.9%)by a bar coating method, thereby to form a functional layer having athickness of 510 μm after drying. The layer was fully dried, pressed ina vacuum and cured at 85° C. for 24 hours, thereby to obtain theelectromagnetic noise suppressor having a thickness of 1120 μm.

Comparative Example 12

A copper foil having a thickness of 100 μm was directly subjected toevaluation to be described later.

(Evaluation)

Examples 17 to 20 and Comparative Examples 11 to 12 were evaluated asfollows.

Observation of cross section was carried out with a transmissionelectron microscope H9000NAR manufactured by Hitachi, Inc.

Electromagnetic noise transmission characteristic: S11 (reflectionattenuation) and S21 (transmission attenuation) were measured by microstrip line (MSL) method using a near field electromagnetic noisesuppressor measuring instrument manufactured by KEYCOM Corporation.

Power loss is a comprehensive index of reflection and transmissioncharacteristics of electromagnetic noise suppressing function determinedby the following equations and takes a value in a range from 0 to 1.Power loss was determined by the following equations based on changes inS11 and S21 of transmission characteristics that were measured as shownin FIG. 33.Power loss (Ploss/Pin)=1—(|Γ|² +|T| ²)S11=20 log|Γ|S21=20 log|T|

Vector network analyzer 37247C manufactured by Anritsu Company Ltd. andtest fixture TF-3A manufactured by KEYCOM Corporation was used formicro-strip line having impedance of 50 Ω.

Electromagnetic noise radiation characteristic: Near fieldelectromagnetic noise radiation characteristic was measured bymicro-loop antenna method using a micro loop 2 mm in diametermanufactured by KEYCOM Corporation and the internal coupling coefficientand mutual coupling coefficient were measured with a spectrum analyzerR3132 manufactured by ADVANTEST CORPORATION.

The results are shown in Table 7, noise transmission characteristics(S11, S21) measured by micro-strip line (MSL) method and power losscharacteristic are shown in FIGS. 31 to 42, and noise attenuationcharacteristics (level of internal coupling and level of mutualcoupling) measured by micro-loop antenna method are shown in FIGS. 43and 44. TABLE 7 Comparative Comparative Example 17 Example 18 Example 19Example 20 Example 11 Example 12 Support layer or PET PI PI None None —film Thickness of 12   9 9 — — — support layer or film (μm) Basematerial Silicone Silicone Silicone Silicone Polyurethane — rubberrubber rubber rubber resin Electrically Ag powder — — — — — conductivefiller (3.5) (particle size, μm) Dielectric Barium Barium Barium — —material powder titanate titanate titanate (particle size, μm) (1.0)(1.0) (1.0) Elastic modulus 8.3 × 10⁸ 6.5 × 10⁷ 1.2 × 10⁷ 6.5 × 10⁷ — —in shear (Pa) Thickness of base 10   10 10 10 500 — material (μm)Magnetic material Fe—Ni Ni Ni Ni Fe—Ni-based — metal powder of flakeshape Magnetic material 30   50 50 50 — — amount (equivalent thickness,nm) Physical vapor Opposing Opposing Opposing Opposing — — depositionmethod target target target target deposition deposition depositiondeposition Surface resistivity   2 × 10² 1.5 × 10³ 1.5 × 10³ 1.5 × 10³ —— (Ω/□) Thickness of Approx. 0.05 Approx. 0.1 Approx. 0.1 Approx. 0.1 —— composite layer (μm) Dielectric material None Ag + Ni Ag + Ni SUS netof SUS net of Cu foil layer 165 mesh 165 mesh Thickness of — 0.125 0.125100 100 100 dielectric material layer (μm) Film formation — PhysicalPhysical — — — vapor vapor deposition on deposition on support filmsupport film Intrinsic 300*   0.07 0.07 (1.2) (1.2) 2 × 10⁻⁶ resistivity(Ω□cm) Thickness of 22   19.125 19.125 110 600 100 electromagnetic noisesuppressor (μm) Specific gravity 2.5 1.3 1.3 2.1 3.3 8.9 FlexibilityRubber-like Flexibility Flexibility Resilience of Thick, heavy, Metalfoil elasticity of support of support metal fabric hard and with goodfilm film prone to flexibility chipping MSL(S11)(dB at −7.07 −6.38 −6.38−7.37 −7.93 — 1 GHz) MSL(S21)(dB at −5.29 −3.93 −4.53 −4.69 −2.29 — 1GHz) Power loss (at 1 GHz)   0.45 0.6 0.55 0.48 0.23 — Near field noiseGood Good Good Good Poor — transmission suppressing effect Micro-loop−5.3  −3.0 −3.5 −6.5 −6.9 +3.5 (Internal coupling coefficient) (dB at0.8 GHz) Micro-loop (Mutual −15.9  −26.5 −24.1 −16.7 −14.6 −36.6coupling coefficient) (dB at 0.8 GHz) Near field noise Good Good GoodGood Good — radiation suppressing effect(*Resistivity of the base material)

The electromagnetic noise suppressors of Examples 17 to 20 have thecomposite layer where part of the base material and the magneticmaterial are integrated, and showed high attenuation characteristic,with the transmission attenuation in a range from −3.93 to −5.29 dB (at1 GHz), in the evaluation of transmission noise by micro-strip linemethod. In terms of power loss, it also showed performance of 0.45 orhigher (at 1 GHz). The electromagnetic noise suppressors of Exampleswere thin and showed specifically high attenuation, in comparison toComparative Example 11 where transmission attenuation was −2.29 dB (at 1GHz) with the functional layer having a thickness of about 500 μm.

In the evaluation of radiation noise by the micro loop antenna method,radiation noise is aggravated by the antenna and resonation at the levelof internal coupling thereby showing positive value, in the metal foilof Comparative Example 12. The electromagnetic noise suppressors ofExamples 17 to 20, suppressing function is demonstrated with values of−3.0 to −6.5 dB (at 0.8 GHz).

Thus, it was shown that the electromagnetic noise suppressors ofExamples 17 to 20 have electromagnetic radiation shielding function, andthey function to suppress the transmission and radiation ofelectromagnetic noise nearby.

It has been also shown that the electromagnetic noise suppressor hassuch a flexibility as can be attached to the inside of a housing of anelectoronic apparatus or directly cover the surface of electroniccomponents or the wiring board whereon electronic components are mountedand, even when made thinner and inserted between wiring boards, cansuppress electromagnetic coupling from increasing due to radiationand/or reflection.

INDUSTRIAL APPLICABILITY

The electromagnetic noise suppressor of the present invention can beused to cover electoronic apparatuses and electronic components, and itallows the manufacture of electoronic apparatuses and electroniccomponents that are smaller and lighter in weight while achievingsufficient electromagnetic noise suppressing effect throughout thesub-microwave band.

1. An electromagnetic noise suppressor comprising: a base materialcontaining a binding agent, and a composite layer consisting of thebinding agent that is a part of the base material and a magneticmaterial, that are integrated with each other.
 2. The electromagneticnoise suppressor according to claim 1, wherein the composite layer isformed by physically vapor-depositing the magnetic material onto thesurface of the base material.
 3. The electromagnetic noise suppressoraccording to claim 1, wherein maximum transmission attenuation ofelectromagnetic radiation per unit thickness of the composite layer isin a range from −0.5 to −500 dB/μm.
 4. The electromagnetic noisesuppressor according to claim 3, wherein maximum transmissionattenuation of electromagnetic radiation is in a range from −10 to −50dB.
 5. The electromagnetic noise suppressor according to claim 3,wherein the maximum reflection attenuation at the frequency wheremaximum transmission attenuation of electromagnetic radiation isachieved is in a range from −6 to −50 dB.
 6. The electromagnetic noisesuppressor according to claim 1, wherein power loss at 1 GHz is in arange from 0.3 to 0.65.
 7. The electromagnetic noise suppressoraccording to claim 1, wherein the thickness of the composite layer is ina range from 0.005 to 20 μm.
 8. The electromagnetic noise suppressoraccording to claim 1, wherein the thickness of the composite layer is ina range from 0.005 to 3 μm.
 9. The electromagnetic noise suppressoraccording to claim 1, wherein the thickness of the composite layer is ina range from 0.005 to 1 μm.
 10. The electromagnetic noise suppressoraccording to claim 1 wherein, the thickness of the composite layer is ina range from 0.005 to 0.3 μm.
 11. The electromagnetic noise suppressoraccording to claim 1, wherein a specific gravity is in a range from 0.9to 1.5.
 12. An electromagnetic noise suppressor comprising a pluralityof the electromagnetic noise suppressors of claim 1 stacked one onanother.
 13. The electromagnetic noise suppressor according to claim 1,wherein the binding agent is a resin or a rubber.
 14. Theelectromagnetic noise suppressor according to claim 2, wherein thebinding agent is a hardening resin.
 15. The electromagnetic noisesuppressor according to claim 2, wherein elastic modulus in shear of thebinding agent is in a range from 1×10⁴ to 1×10¹⁰ Pa.
 16. Theelectromagnetic noise suppressor according to claim 2, wherein elasticmodulus in shear of the binding agent is in a range from 1×10⁴ to 5×10⁷Pa.
 17. The electromagnetic noise suppressor according to claim 1,further comprising: a heat conduction layer containing a thermallyconductive filler.
 18. The electromagnetic noise suppressor according toclaim 1, further comprising: a support layer.
 19. The electromagneticnoise suppressor according to claim 1, wherein the base materialcontains a non-halogen and non-antimony flame retarding agent.
 20. Theelectromagnetic noise suppressor according to claim 1, furthercomprising: a flame retarding resin layer.
 21. The electromagnetic noisesuppressor according to claim 1, wherein the base material contains anelectrically conductive filler.
 22. The electromagnetic noise suppressoraccording to claim 21, wherein the electrically conductive filler is atleast one kind of electrically conductive fine powder selected from thegroup consisting of metal powder, metal fiber, metal-coated fineparticles, fine carbon particles and carbon nano-tube.
 23. Theelectromagnetic noise suppressor according to claim 1, furthercomprising: an electrically conductive layer.
 24. The electromagneticnoise suppressor according to claim 23, wherein the electricallyconductive layer is at least one kind selected from the group consistingof metal foil, fabric of metal fibers, fabric of electrically conductivefibers, interlaced metal wires, interlaced electrically conductivefibers, organic polymer layer containing an electrically conductivefilling agent dispersed therein and electrically conductive film. 25.The electromagnetic noise suppressor according to claim 24, wherein theelectrically conductive film comprises a support film and a metal layerhaving a thickness from 5 to 500 nm formed by physical deposition of ametal on the support film.
 26. The electromagnetic noise suppressoraccording to claim 25, wherein the metal layer is formed by opposingtarget type magnetron sputtering process.
 27. The electromagnetic noisesuppressor according to claim 1, wherein the base material contains adielectric material powder.
 28. The electromagnetic noise suppressoraccording to claim 27, wherein the dielectric material powder is atleast one kind selected from the group consisting of bariumtitanate-based ceramic, zirconium titanate-based ceramic and leadperovskite-based ceramic.
 29. A method of manufacturing anelectromagnetic noise suppressor, which comprising: a vapor depositionprocess of physically vapor-depositing a magnetic material onto thesurface of a base material containing a binding agent to form acomposite layer on the surface of the base material.
 30. The method ofmanufacturing an electromagnetic noise suppressor according to claim 29,wherein the magnetic material is deposited on the surface of the basematerial containing the binding agent by physical vapor deposition ofopposing target type magnetron sputtering process.
 31. The method ofmanufacturing the electromagnetic noise suppressor according to claim29, wherein the magnetic material is deposited on the surface of thebase material containing the binding agent by physical vapor depositionwith particle energy of 5 to 1000 eV.
 32. The method of manufacturingthe electromagnetic noise suppressor according to claim 29, wherein theamount of the magnetic material deposited is in a range from 0.5 to 200nm in terms of equivalent thickness of the magnetic material film.
 33. Amethod of manufacturing an electromagnetic noise suppressor, whichcomprises: a stack fabricating process of fabricating a stack bystacking other layers on a base material containing a binding agent, anda vapor deposition process of physically vapor-depositing a magneticmaterial onto the surface of the base material containing a bindingagent to form a composite layer on the surface of the base material. 34.An article with an electromagnetic noise suppressing function wherein atleast a part of the surface of the article is covered by theelectromagnetic noise suppressor of claim
 1. 35. The article with anelectromagnetic noise suppressing function of claim 34, wherein thearticle is an electronic component.
 36. The article with anelectromagnetic noise suppressing function according to claim 34,wherein the article is a printed wiring board on which electroniccomponents are mounted.
 37. The article with an electromagnetic noisesuppressing function according to claim 36, wherein the printed wiringboard is a flexible printed wiring board.
 38. The article with anelectromagnetic noise suppressing function according to claim 34,wherein the article is an electric connector.
 39. The article with anelectromagnetic noise suppressing function according to claim 38,wherein the electric connector is a flexible connector.
 40. The articlewith an electromagnetic noise suppressing function according to claim34, wherein the article is a flat cable.
 41. The article with anelectromagnetic noise suppressing function according to claim 34,wherein the article is a key top member for pushbutton switch.
 42. Thearticle with an electromagnetic noise suppressing function according toclaim 34, wherein the article is an insert sheet for a preform.
 43. Thearticle with an electromagnetic noise suppressing function according toclaim 34, wherein the article is a semiconductor integrated circuit. 44.A method of manufacturing an article with an electromagnetic noisesuppressing function, which comprises: a coating process of coating atleast a part of the article with a base material containing a bindingagent, and a vapor deposition process of physically vapor-depositing amagnetic material onto the surface of a base material containing abinding agent to form a composite layer on the surface of the basematerial